Application of the experimental watershed approach to advance urban watershed precipitation/discharge understanding

Reliable methods are required to provide the detailed hydrologic information necessary to improve management of water resources and aquatic ecosystems in developing/urbanizing watersheds. A case study was implemented in a representative 230 km² mixed-use, urbanizing watershed to advance precipitation/discharge understanding. Precipitation and streamflow were monitored in five sub-watersheds (nested-scale experimental watershed study design), partitioned by dominant land use type. Data were collected at 30-min intervals through the 2009 to 2015 water years. Individual sub-watershed area-normalized flow and runoff coefficients differed by as much as 400%. Two high density, urban sub-watersheds displayed large runoff coefficients indicating disproportionately high flow response to precipitation inputs. Regression analyses of sub-watershed land use characteristics and flow metrics showed strong (i.e. R² > 0.9) statistically significant (p < 0.05) linear relationships for percentage developed, forest, and agriculture land cover. Observed relationships between land use and flow metrics illustrate the complexity of contrasting and intermingled land use types in urbanizing, mixed-land-use watersheds. Results highlight the variable hydrologic impacts of land use and suggest the potential for vegetation management as a tool for streamflow mediation in urban settings. The work is one of the first to utilize the experimental watershed method to isolate and quantify land use impacts in the context of a contemporary mixed-land-use watershed. Collectively, results emphasize the utility of the method for land and water resource managers seeking science-based information to guide management decisions and more effectively target remediation efforts in contemporary multiple-land-use watersheds.     

Direct and indirect effects of human population density and land use on physical features and invertebrates of Iowa (U.S.A.) streams

To improve understanding of human impacts on headwater stream condition, we quantified relationships between human, terrestrial landscape, and stream system variables in 29 central Iowa watersheds. Across study watersheds, between 0 and 100 % of total land area was characterized as “urban” (developed and barren land), whereas cultivated land constituted between 0 and 71 % of watershed area. Several variables were measured for each stream and associated watershed. Strengths of correlative relationships were used to select variables for path analysis, which we used to gain insight into factors affecting stream condition by evaluating direct and indirect effects of human system variables, terrestrial landscape variables, and physical stream variables on stream invertebrates. Results indicated that in predominantly urban watersheds, contaminant inputs to streams (measured by streamwater conductivity) negatively affected invertebrates, including EPT taxa (Ephemeroptera, Plecoptera, Trichoptera), and streamwater contaminant concentrations increased with impervious surface and human population density in the watershed. In rural watersheds, high streamwater nitrogen concentrations associated with cultivated land were related to declines in invertebrate taxon richness. Independent of land use, invertebrate abundance and taxonomic diversity were positively related to coarse substrate abundance on the streambed. Additionally, stream flow (discharge) increased with watershed area, which in turn increased invertebrate taxonomic diversity. Apparently, mechanisms responsible for human impacts on stream condition in central Iowa depend on dominant land use in the watershed. Additionally, stream ecosystems with high quality benthic habitat, and those located in large watersheds with greater flow, appear to be more resilient to land use effects.     

Effects of urbanization and land use on fish communities in Valley Creek watershed, Chester County, Pennsylvania

Valley Creek watershed, located in southeastern Pennsylvania, is a small, fourth-order stream that empties into the Schuylkill River at Valley Forge National Historic Park, thirty-five kilometers northwest of Philadelphia. The 64 km² watershed has been under extreme urbanization pressure over the past 30 years, resulting in rapidly increasing impervious surface cover and decreasing open space. The purpose of this study was to document some of the effects of urbanization on fish assemblages by quantifying the fish communities at fifteen sites throughout the watershed. Long-term effects of continued urbanization were identified, as data from the present study were compared to similar work completed nearly ten years earlier. There has been a shift in species composition from intolerant, coldwater species to more tolerant, eurythermal species. Currently, Valley Creek is supporting a naturally reproducing population of brown trout, but there has been a marked decline in relative abundance and range since 1993. Increased stream temperature from urban run-off is one of the primary issues in Valley Creek. Species composition was unique at each of the 15 stations owing to the effect of local land use in each station’;s drainage area. Fish assemblages revealed a patchy, non-continuous pattern of fish distribution.     

Spatiotemporal patterns of urbanization over the past three decades: a comparison between two large cities in Southwest China

China’s economic development over the past three decades has been remarkable due to the establishment of the “Reform and Opening-up” program. Meanwhile, urbanization, one of the most intensive human activities, has significantly changed the land cover across China. Here we used remote sensing data and landscape metrics to explore the spatiotemporal patterns of urbanization in two large Chinese cities, Chengdu (1978–2010) and Chongqing (1976–2010). Results suggested that urban land in both cities experienced a significant growth and became 9.8 and 6.3 times larger than the initial for Chengdu and Chongqing, respectively. The edge-expansion was the major urban growth form for both cities, accounting for more than 40 % of total three types (i.e., edge-expansion, infilling, and outlying) although fluctuating during the whole period. Both cities started a spurt growth in the 1990s although the starting times were different (1992 and 1996 for Chengdu and Chongqing, respectively) because of different policies. Spatial distribution of the newly developed urban lands was largely constrained by topography. Landscape analysis not only revealed an increasing fragmentation and complexity in the study area under the impact of urbanization, but also tested the hypothesis on urbanization patterns.     

Urbanization impacts on the structure and function of forested wetlands

The exponential increase in population has fueled a significant demographic shift: 60% of the Earth's population will live in urban areas by 2030. While this population growth is significant in its magnitude, the ecological footprint of natural resource consumption and use required to sustain urban populations is even greater. The land use and cover changes accompanying urbanization (increasing human habitation coupled with resource consumption and extensive landscape modification) impacts natural ecosystems at multiple spatial scales. Because they generally occupy lower landscape positions and are linked to other ecosystems through hydrologic connections, the cascading effects of habitat alteration on watershed hydrology and nutrient cycling are particularly detrimental to wetland ecosystems. I reviewed literature relevant to these effects of urbanization on the structure and function of forested wetlands. Hydrologic changes caused by habitat fragmentation generally reduce species richness and abundance of plants, macroinvertebrates, amphibians, and birds with greater numbers of invasives and exotics. Reduction in soil saturation and lowered water tables result in greater nitrogen mineralization and nitrification in urban wetlands with higher probability of NO^– ₃ export from the watershed. Depressional forested wetlands in urban areas can function as important sinks for sediments, nutrients, and metals. As urban ecosystems become the predominant human condition, there is a critical need for data specific to urban forested wetlands in order to better understand the role of these ecosystems on the landscape.     

Comparison of decapod communities across an urban-forest land use gradient in Puerto Rican streams

Urbanization influences a range of factors related to stream health, including the hydrologic regime, water quality, and riparian conditions that lead to negative effects on terrestrial and aquatic ecosystems. However, impacts on freshwater decapods from urbanization of tropical streams have not been reported. We hypothesized that changes in decapod communities in watersheds with different levels of urbanization are related to changes in physical stream habitats caused by different land uses and their effects on water discharge. The impacts of land use on the physico-chemical characteristics of streams and freshwater decapod communities were evaluated in three watersheds characterized by low, moderate and high-intensities of urbanization in Puerto Rico. For the low and moderately developed urban watersheds, decapod species richness ranged from 10 to 11 species; the highly urbanized watershed only had 4 species. Macrobrachium faustinum and Xiphocaris elongata were the most ubiquitously species and were found in all watersheds. Multivariable analysis of physical characteristics and densities of the decapod families resulted in one axis that explained 80 % of the total variation among the watersheds and was correlated with stream discharge. The effect of discharge is likely a result of frequent high flows that sustain habitats with high concentrations of dissolved oxygen and low concentrations of pollutants. An increase in physico-chemical parameters were observed from the LUW to the HUW. These results indicate that the decapod communities were most likely influenced by land use and environmental conditions that affected erosional aspects related to water discharge and water quality in the highly impacted watersheds.     

Effect of urbanization on surface water chemistry in south-central Texas

The use of state factors can adequately describe the biogeochemistry and geochemistry of relatively undisturbed surface waters. Watersheds with increasing proportions of urban and suburban land use, particularly in sub-tropical, semi-arid and arid urban areas, that utilize irrigation for turfgrass and landscaping may have a low flow urban signature that relates to the source water used by municipal water suppliers. We examined thirteen watersheds; four with waste water treatment plants (24–67% urbanization), four rural (< 30% urbanization) and five urban (> 30% urbanization) in a humid sub-tropical oak savannah in south-central Texas. Three of our urban and one of our rural watersheds displayed the signature of municipal tap water. Three out of four watersheds with waste water treatment plants displayed the signature of treated sewage effluent. We suggest as a result of this study that the chemistry of municipal tap water particularly that with high sodium and bicarbonate, used in urban watersheds for irrigating turfgrass and landscapes may have detrimental effects on base flow stream water quality after it has interacted with watershed soils.     

Establishing turf grass increases soil greenhouse gas emissions in peri-urban environments

Urbanization is becoming increasingly important in terms of climate change and ecosystem functionality worldwide. We are only beginning to understand how the processes of urbanization influence ecosystem dynamics and how peri-urban environments contribute to climate change. Brisbane in South East Queensland (SEQ) currently has the most extensive urban sprawl of all Australian cities. This leads to substantial land use changes in urban and peri-urban environments and the subsequent gaseous emissions from soils are to date neglected for IPCC climate change estimations. This research examines how land use change effects methane (CH₄) and nitrous oxide (N₂O) fluxes from peri-urban soils and consequently influences the Global Warming Potential (GWP) of rural ecosystems in agricultural use undergoing urbanization. Therefore, manual and fully automated static chamber measurements determined soil gas fluxes over a full year and an intensive sampling campaign of 80 days after land use change. Turf grass, as the major peri-urban land cover, increased the GWP by 415 kg CO₂-e ha^?1 over the first 80 days after conversion from a well-established pasture. This results principally from increased daily average N₂O emissions of 0.5 g N₂O ha^?1 d^?1 from the pasture to 18.3 g N₂O ha^?1 d^?1 from the turf grass due to fertilizer application during conversion. Compared to the native dry sclerophyll eucalypt forest, turf grass establishment increases the GWP by another 30 kg CO₂-e ha^?1. The results presented in this study clearly indicate the substantial impact of urbanization on soil-atmosphere gas exchange in form of non-CO₂ greenhouse gas emissions particularly after turf grass establishment.     

Using macroinvertebrate assemblages and multiple stressors to infer urban stream system condition: a case study in the central US

Characterizing the impacts of hydrologic alterations, pollutants, and habitat degradation on macroinvertebrate species assemblages is of critical value for managers wishing to categorize stream ecosystem condition. A combination of approaches including trait-based metrics and traditional bioassessments provides greater information, particularly in anthropogenic stream ecosystems where traditional approaches can be confounded by variously interacting land use impacts. Macroinvertebrates were collected from two rural and three urban nested study sites in central Missouri, USA during the spring and fall seasons of 2011. Land use responses of conventional taxonomic and trait-based metrics were compared to streamflow indices, physical habitat metrics, and water quality indices. Results show that biotic index was significantly different (p?<?0.05) between sites with differences detected in 54 % of trait-based metrics. The most consistent response to urbanization was observed in size metrics, with significantly (p?<?0.05) fewer small bodied organisms. Increases in fine streambed sediment, decreased submerged woody rootmats, significantly higher winter Chloride concentrations, and decreased mean suspended sediment particle size in lower urban stream reaches also influenced macroinvertebrate assemblages. Riffle habitats in urban reaches contained 21 % more (p?=?0.03) multivoltine organisms, which was positively correlated to the magnitude of peak flows (r ²?=?0.91, p?=?0.012) suggesting that high flow events may serve as a disturbance in those areas. Results support the use of macroinvertebrate assemblages and multiple stressors to characterize urban stream system condition and highlight the need to better understand the complex interactions of trait-based metrics and anthropogenic aquatic ecosystem stressors.     

Environmental and social predictors of phosphorus in urban streams on the Island of Montréal,Québec

Researchers have identified the importance of social characteristics for understanding ecological patterns in cities but the use of these characteristics in urban stream research has yet to be fully explored. Urban development is currently the second-largest cause of stream impairment in North America due in part to nutrient loading. However, research into factors that influence nutrient concentrations in urban streams is lacking. We sampled seven streams on the island of Montréal daily to measure phosphorus (P) concentration and P flux in each stream. We then compared stream P concentration and flux to several watershed characteristics commonly used to predict stream nutrients (e.g., watershed imperviousness, land use, existence of a riparian buffer) as well as several socio-economic characteristics of the watersheds (e.g., average home value, median household income). Overall, impervious surface cover and measures of land use were most effective at explaining the variation in P concentration and P flux in streams on the island of Montréal, while the riparian buffer and socio-economic variables were less effective. However, dollars spent on fertilizer per hectare of residential land and percent residential land use became important predictors of stream P concentration when impervious surface cover was removed from the regression model. This suggests that after accounting for the impact of physical watershed characteristics, social factors may be important predictors of urban stream P concentration. The results of our study suggest that more research is needed to determine the role that socio-economic variables play with respect to urban stream P.     

Characterizing the urban environment through urban morphology types (UMTs) mapping and land surface cover analysis: the case of Addis Ababa,Ethiopia

Characterizing the urban environment through urban morphology types (UMTs) can help to decide on what parts of urban areas should be conserved. The aim of this study was to map and detect changes in UMTs and land surface cover in the city of Addis Ababa. UMT maps for 2006 and 2011 were produced by digitizing ortho-rectified aerial photographs. Eleven higher level and 35 detailed UMTs were identified as the basis for the study. Within the defined higher levels of UMTs in 2006, the most dominant UMT was agriculture covering 38 % of the total area while in 2011 residential UMTs stand out with the highest land coverage (33.3 %) indicating rapid conversion of other land uses to residential category. Land surface cover analysis used 12 surface cover categories.Change analysis between 2006 and 2011 revealed that surface cover types of built structure type I (generally well planned and high rise buildings), non-eucalyptus trees, dark bare-ground, light bare-ground and vegetable farm showed positive change whereas built structure type II (informal, generally unplanned, and non-high rise buildings), eucalyptus trees, shrub/bush vegetation, grassland and field crop cover showed negative change. The results also showed that almost half of the land surface cover of Addis Ababa could be considered to be evapotranspiring. To maintain a balanced urban environment, all green spaces in the city should be ecologically networked and the planning of green space should aim to ensure that principles of multi-functionality are followed as the city continues to undergo rapid urbanization.     

Ecological consequences of fragmentation and deforestation in an urban landscape: a case study

Landscape change is an ongoing process even within established urban landscapes. Yet, analyses of fragmentation and deforestation have focused primarily on the conversion of non-urban to urban landscapes in rural landscapes and ignored urban landscapes. To determine the ecological effects of continued urbanization in urban landscapes, tree-covered patches were mapped in the Gwynns Falls watershed (17158.6?ha) in Maryland for 1994 and 1999 to document fragmentation, deforestation, and reforestation. The watershed was divided into lower (urban core), middle (older suburbs), and upper (recent suburbs) subsections. Over the entire watershed a net of 264.5 of 4855.5?ha of tree-covered patches were converted to urban land use??125 new tree-covered patches were added through fragmentation, 4 were added through reforestation, 43 were lost through deforestation, and 7 were combined with an adjacent patch. In addition, 180 patches were reduced in size. In the urban core, deforestation continued with conversion to commercial land use. Because of the lack of vegetation, commercial land uses are problematic for both species conservation and derived ecosystem benefits. In the lower subsection, shape complexity increased for tree-covered patches less than 10?ha. Changes in shape resulted from canopy expansion, planted materials, and reforestation of vacant sites. In the middle and upper subsections, the shape index value for tree-covered patches decreased, indicating simplification. Density analyses of the subsections showed no change with respect to patch densities but pointed out the importance of small patches (??5?ha) as ??stepping stone?? to link large patches (e.g., >100?ha). Using an urban forest effect model, we estimated, for the entire watershed, total carbon loss and pollution removal, from 1994 to 1999, to be 14,235,889.2?kg and 13,011.4?kg, respectively due to urban land-use conversions.     

A GIS for environmental assessment of air pollution impacts on urban clusters and natural landscape at Rosetta City and region,Egypt

An air pollution problem is taking place in the Rosetta region resulting from the brick industry. Polluting point sources cause plumes that disperse by the prevailing wind, covering urban areas of Rosetta City and surrounding landscape of agricultural fields. A model for pollutants plumes was designed through a GIS to calculate the dispersal of total suspended particulate (TSP) loads over the landscape and to estimate its spatial distribution and to analyze its relationship with other geographic land use attributes.TSP pollutant concentrations starting from 100 g/m³ cover more than 34 km² of sensitive land cover through all the year. A concentration level of 100 g/m³ affects about 93% of the sensitive palm trees cultivation, 47% of cultivated land, and 92% of urban areas. TSP concentration level of 200 g/m³ was found to be affecting the same percentage of built-up urban areas.Concentration levels exceed the permissible limits mentioned in the Egyptian law of environment (90 g/m³). The situation is hygienically deteriorated, and large areas of agricultural land are strongly affected or subjected to future impact. Recommended measures are mostly involved with transferring this industrial activity to a safer location at the southwest of the city. The study proposes that brick mills sites on the river Nile bank be utilized for urban development projects and for the promotion of tourism.     

Urbanization-related distribution patterns and habitat-use by the marine mesopredator,giant Pacific octopus (<Emphasis Type="Italic">Enteroctopus dofleini</Emphasis>)

Urbanization is a process that heavily alters marine and terrestrial environments, though terrestrial urban ecosystems have been studied far more intensively. Terrestrial studies suggest that urbanization can facilitate mesopredators by enhancing food and shelter resources and reducing predation pressure from apex consumers. This in turn has considerable consequences for ecological communities. We evaluated spatial distribution patterns and habitat-use of the marine mesopredator, giant Pacific octopus (Enteroctopus dofleini), relative to terrestrial urbanization intensity in Puget Sound, Washington, USA. Using field surveys and citizen-contributed data for E. dofleini, we examined whether: (1) Distribution was related to urbanization, (2) Abundance was related to the extent of benthic anthropogenic debris, and (3) Diet differed as a function of urbanization and den cover. Our results suggest that urbanization impacts may differ with depth. Mixed-effects logistic regression model estimates for the probability of occurrence increased with urbanization in deep-water (> 24 m), and decreased with urbanization in shallow water (< 18 m). Accompanying field surveys indicated that E. dofleini abundance was correlated with the number of benthic anthropogenic debris items, and that E. dofleini diets were not affected by urbanization intensity or den cover. Though E. dofleini may be synanthropic within certain urban environments, the mechanisms driving this pattern likely differ from those affecting common urban mesopredators on land, with den provisioning from man-made structures being more important than altered food resources.     

Connecting local environmental knowledge and land use practices: A human ecosystem approach to urbanization in West Georgia

Issues of urban sprawl and migration of exurban residents into the surrounding countryside of metropolitan areas have generated considerable debate across the US. These debates often revolve around the ecological footprint of urban areas and the erosion of quality of life indicators associated with rapid expansion of urban and residential areas. Although there has been much research done on the environmental and socioeconomic impacts of urbanization, little attention has been given to cultural impacts. This paper focuses specifically on the role of local environmental knowledge as an important resource in human ecosystems, and looks at the implications of environmental knowledge loss associated with urbanization and its related demographic changes. We compared environmental knowledge among rural, urban, and developing watersheds in western Georgia, and also look at relationships between local environmental knowledge and variables such as gender, education, income, and participation in outdoor recreational activities. We then explored how variations in environmental knowledge affected land use practices at the household level. The mean knowledge scores of residents in all three classifications of rural watersheds were higher than those living in developing and urban watersheds. We found residents of managed pine watersheds possessed the highest mean scores (p = 0.006), while urban watershed residents were the lowest. We also found that local environmental knowledge was influenced by active participation in outdoor recreation, with active bird-watchers having the highest environmental knowledge scores. However, we found less influence of factors such as education and income on environmental knowledge. We also found a clear connection between local environmental knowledge and land management practices. Timber owners scored higher than non-timber owners (p = 0.099), and landowners who constructed streamside management zones (SMZs) scored higher than those who did not (p = 0.034).     

Long-term urbanization effects on tree canopy cover along an urban–rural gradient

Urban forestry can benefit from improved knowledge of urbanization??s effects on tree canopy cover (TCC), a prominent urban forest indicator. This study examined changes in TCC over a long time frame, with respect to land cover (LC) changes, and across municipal boundaries. Specifically, I used air photos at 14 dates from 1937 to 2009 to develop an exceptionally long record of TCC change in Minnesota??s Twin Cities Metropolitan Area. During the study period overall TCC nearly doubled from 17% to 33% while the proportion urban land cover rose by 47%, highlighting the opportunity for substantial TCC gains following urbanization in previously agricultural landscapes, even in regions that were forested prior to European settlement. Results demonstrate that more intensely developed sites generally had lower TCC, and older urban sites had higher TCC. Modern TCC was not adequately characterized by linear distance along the urban?Crural gradient, but instead peaked near the center of the gradient where mature residential neighborhoods are prevalent. Compared to other land cover changes, urbanization events caused the highest rate of immediate TCC loss (9.6% of events), yet urban areas had the second highest TCC (>35%) in 2009, indicating that urban land gained TCC relatively efficiently following development. The results of this study provide new historical context for urban forest management across an urban?Crural gradient, and emphasize the need to consider ecological legacies and temporal lags following land cover changes when considering TCC goals in urban settings.     

Modeling above-ground carbon storage: a remote sensing approach to derive individual tree species information in urban settings

Vegetation has gained importance in respective debates about climate change mitigation and adaptation in cities. Although recently developed remote sensing techniques provide necessary city-wide information, a sufficient and consistent city-wide information of relevant urban ecosystem services, such as carbon emissions offset, does not exist. This study uses city-wide, high-resolution, and remotely sensed data to derive individual tree species information and to estimate the above-ground carbon storage of urban forests in Berlin, Germany. The variance of tree biomass was estimated using allometric equations that contained different levels of detail regarding the tree species found in this study of 700 km², which had a tree canopy of 213 km². The average tree density was 65 trees/ha per unit of tree cover and a range from 10 to 40 trees/ha for densely urban land cover. City-wide estimates of the above-ground carbon storage ranged between 6.34 and 7.69 tC/ha per unit of land cover, depending on the level of tree species information used. Equations that did not use individually localized tree species information undervalued the total amount of urban forest carbon storage by up to 15 %. Equations using a generalized estimate of dominant tree species information provided rather precise city-wide carbon estimates. Concerning differences within a densely built area per unit of land cover approaches using individually localized tree species information prevented underestimation of mid-range carbon density areas (10–20 tC/ha), which were actually up to 8.4 % higher, and prevented overestimation of very low carbon density areas (0–5 tC/ha), which were actually up to 11.4 % lower. Park-like areas showed 10 to 30 tC/ha, whereas land cover of very high carbon density (40–80 tC/ha) mostly consisted of mixed peri-urban forest stands. Thus, this approach, which uses widely accessible and remotely sensed data, can help to improve the consistency of forest carbon estimates in cities.     

Potential nitrogen mineralization responses of urban and rural forest soils to elevated temperature in Louisville,KY

Soil nitrogen (N) mineralization is an important process determining terrestrial N availability, and evidence suggests elevated temperatures will enhance N mineralization rates. Along a 40 km urban-rural gradient of chestnut oak forest stands in Louisville, KY, we expected N mineralization rates would be higher in urban than in rural forests in part due to increased temperatures caused by the urban heat island. However, a 12-month field study along this Louisville gradient showed that annual N mineralization rates were lower in urban than in rural stands. Since variation in precipitation inputs and other factors across this land-use gradient may be influencing soil N mineralization rates, we conducted a three-month soil incubation experiment in the lab to determine the extent to which a + 2 °C temperature difference could affect soil N mineralization in urban and rural soils. Across the range of temperatures tested, rural soils mineralized N at twice the rate of urban soils under base (7.86 vs. 3.65 mg N kg^?1 AFDW soil d^?1) and elevated (9.08 vs. 4.76 mg N kg^?1 AFDW soil d^?1) temperatures (p < 0.01). A 2 °C temperature difference, did not significantly alter total inorganic N production in urban (p = 0.272) or rural soils (p = 0.293). The proportion of nitrate produced was lower in the urban (15.1 %) than in the rural soils (72.3 %; p < 0.01). These results suggest that differences in soil organic matter quality and potentially decomposer community composition are the primary explanatory factors for forests along this Louisville gradient.     

Detection of biotic responses to urbanization using fish assemblages from small streams of western Georgia,USA

We examined relationships between stream fish assemblages and land use alteration associated with urbanization in 15 lower Piedmont watersheds along an urbanization gradient north of Columbus, western Georgia. Based on land cover data from 2002 Landsat 7 TM imagery aerial photos, streams drained watersheds that were largely urban, developing (suburban), agricultural (pasture), managed pine forest, and unmanaged mixed-forest. We quantified fish seasonally from 3 run-pool segments in each stream, and used a variety of metrics as response variables in analyses of relationships between fish assemblage structure and land use and natural basin variation. In general, Georgia-Index of Biotic Integrity (GA-IBI) values, Bray-Curtis faunal similarity of streams to mean conditions within reference streams, proportions of fish as lithophilic spawners, and fish lacking eroded fins, lesions, tumors decreased with increasing urbanization. Multiple regression indicated that assemblages were explained by a combination of land use and natural basin variables (basin size, average discharge, nearest distance to a larger downstream tributary [colonization source]), with land use variables being important predictors of summer assemblages and natural basin variables being more important in winter and spring assemblages. Non-metric multidimensional scaling (NMDS) ordinations revealed strong separation between assemblages in urban watersheds and forested watersheds, whereas assemblages in agricultural and developing watersheds were intermediate between those in urban and forested watersheds. Our data suggest that fish are reliable indicators of anthropogenic disturbance at the landscape scale, at least seasonally, and may be used to forecast the magnitude of landscape-level changes in stream structure and function associated with the conversion of forests to urban/suburban land in the Southeast.     

Assessment of landscape patterns affecting land surface temperature in different biophysical gradients in Shenzhen, China

The urban heat island (UHI) effect is one of the important ecological effects of urbanization. This study focuses on the different effects of landscape patterns on LST within different land covers. The land cover was measured by surface biophysical components, including vegetation fraction (VF) and impervious surface area (ISA), acquired by a linear spectral mixture model (LSMM). LST was derived from Landsat-5 TM thermal infrared (TIR) data using the generalized single-channel method. Landscape patterns were measured by landscape metrics, including the Shannon diversity index (SHDI), the aggregation index (AI), patch density (PD), and fractal dimension area-weighted mean index (FRAC_AM). Shenzhen, a rapidly urbanizing city in China, was taken as the case study area. Results showed that VF and ISA are more important than spatial patterns in determining LST. However, these effects change in densely covered areas. VF and LST are negatively correlated, with the inflection of the regression curves being 45 %. In areas with VF lower than 45 %, the correlation between LST and VF is monotonically linear. In areas with VF higher than 45 %, landscape patterns can act to decrease LST. The aggregation index (AI) and the largest patch index (LPI) can contribute to decreasing LST significantly. Impervious surfaces contribute to high temperature, and the inflection point of the regression curves is 70 %. In areas with ISA higher than 70 %, a fragmented pattern of impervious surfaces can lower LST. These findings provide insights for planners into how the strategic use of landscape to mitigate UHI effects may vary for different land covers.