Urban Watersheds Research Articles

Anthropogenic activity remains the main contributor to fecal pollution in managed tropical watersheds as unraveled by PhyloChip microarray-based microbial source tracking

The spread of disease by enteric pathogens associated with fecal contamination is a major concern for the management of urban watersheds. So far, the relative contribution of natural and anthropogenic sources to fecal pollution in managed tropical watersheds remains poorly evaluated. In this study, the microbiomes of water samples collected from managed watersheds in Singapore were elicited using the PhyloChip, a dense 16S rRNA gene-based DNA microarray, and fecal impairment was inferred using a machine-learning classification algorithm (SourceTracker). The predicted contribution of wildlife fecal sources to environmental samples was generally negligible (< 0.01 ± 0.01), indicating a low likelihood of fecal impairment from natural sources. However, sewage showed considerably higher contribution (0.09 ± 0.05) to microbial communities in a subset of watershed samples from canals and rivers, suggesting persistent impairment of certain areas by anthropogenic activity although being managed. Interestingly, the contribution of sewage microbial communities showed decreasing trends from canals/rivers to the connected reservoirs, indicating meaningful auto-mitigation of fecal pollution in canals and rivers. Notably, exclusion of locally derived fecal samples and source categories from the training data set impaired the predictive performance of the classification algorithm despite a high degree of similarity in the phylogenetic composition of microbiomes in biologically similar but geographically distinct sources.

Quantifying health risks of plastisphere antibiotic resistome and deciphering driving mechanisms in an urbanizing watershed

Microplastics (MPs) ubiquitous in environments promote the dissemination of antibiotic resistance genes (ARGs), threatening ecosystem safety and human health. However, quantitative assessments of the health risks of ARGs (HRA) in plastisphere and an in-depth exploration of their driving mechanisms are still lacking. Here, the microbiomes, ARGs, and community assembly processes of five types of MPs in an urbanizing watershed were systematically investigated. By fully considering the abundance, clinical availability, human pathogenicity, human accessibility, and mobility of 660 ARGs in plastisphere, the HRA on MPs were quantified and compared. Polyethylene had the highest HRA among the five MP types, and urbanization further increased its risk index. In addition to abiotic factors, more complex biotic factors have been shown to drive HRA in plastisphere. Specifically, dispersal limitation accounted for the increasing diversity and interaction of bacteria that determined HRA in plastisphere. Further analysis of metabolic functions indicated that a higher HRA was accompanied by decreased normal metabolic functions of plastisphere microbiota due to the higher fitness costs of ARGs. This study advances the quantitative surveillance of HRA in plastisphere and understanding of its driving mechanisms. This will be helpful for the management of both MPs and ARGs treatments for human health.

Development of a Simple Design Method for an Infiltration Facility using Curve Number

As climate change accelerates, the scale and intensity of natural disasters are increasing, and the frequency of localized heavy rains is increasing rapidly. Urban watersheds have a high ratio of impervious areas. So there is a high possibility of flooding in the event of torrential rain, and large-scale damage can occur because the population and material resources are highly concentrated. River improvements, sewerage maintenance, and rainwater storage installations are frequently used to reduce flood damage. More recently, low-impact development (LID) techniques have been proposed; however, LID facilities are installed on a small scale and in various locations. In addition, they require many parameters for a rainfall-runoff analysis; consequently, the design of these facilities require too much manpower and time. In this study, we analyze the rainfall-runoff reduction effect based on the size of a facility to present a simpler, more efficient design method. Next, the curve number (CN) corresponding to the capacity of each facility is estimated and the correlation between the facility’s area ratio and the CN is analyzed. As a result, a relational expression that can calculate the new CN with the same rainfall-runoff reduction effect as the installed LID facility was derived by using the CN before the installation of the LID facility and the facility area ratio. Thus, we present a simple design method using the recalculated CN without directly entering LID facilities into a storm water management model (SWMM).

Spatiotemporal evolution law and driving mechanism of production–living–ecological space from 2000 to 2020 in Xinjiang, China

Xinjiang is located in the northwest of China, with a vast territory and abundant resources, which holds an important strategic position for China. However, the climate in the region is arid and the ecological environment is fragile. In recent years, with the growth of population and the improvement of economic development level, construction and agricultural land in Xinjiang have gradually expanded, and ecological land has been extensively occupied. The competition between land resources is becoming increasingly fierce, leading to some ecological and environmental problems in the region. In this context, understanding the spatiotemporal changes and driving factors of Xinjiang's production space, living space and ecological space (PLES) is of great practical significance for promoting sustainable development in the region, and can also provide reference for the research of PLES in other arid areas at home and abroad. At present, most of the research on PLES is focused on small-scale areas such as urban agglomerations, rural areas, and watersheds, or non arid areas with relatively superior natural conditions, with less research on large-scale arid areas. In this study, the transfer matrix, the center of gravity movement trajectory, Moran's I and the spatial conflict measurement model were used to illustrate the spatial–temporal evolution of PLES in Xinjiang, and the correlation coefficient was used to determine the main factors affecting the change of PLES. Results show that (1) Xinjiang is dominated by ecological space, which accounts for more than 90% of the total area of Xinjiang and has significant continuity. They are mainly distributed in Tarim, Turpan, and the northern Junggar Basin. The production space area accounts for about 5% of the total area of Xinjiang and is distributed in the vicinity of the Tianshan and Kunlun Mountains. Living space accounts for about 1% of Xinjiang's total area and is scattered around cities. (2) From 2000 to 2020, the change degree of PLES in Xinjiang in the last decade is higher than that in the first decade, most of which is the transformation from ecological space to production space. The three types of spaces influence and restrict each other in the development process. (3) Population, crop sown area, natural conditions, policy and the development level of agricultural science and technology are the main factors affecting the spatial distribution of production. Environmental factors such as altitude, soil erosion and temperature have a great influence on ecological space. Population, the output value of various industries and total retail sales of consumer goods are the main factors affecting residential space. The evolution of Xinjiang PLES is the result of multiple factors. (4) The medium spatial conflict dominates, mainly distributed in Tarim Basin and Junggar Basin. The weak and strong space conflicts are concentrated in the oases in the north of the Tianshan and Kunlun Mountains, and the number is small. From 2000 to 2020, the increasing degree of spatial conflicts in Xinjiang is due to land desertification.

Sediment’s production in coastal urban watersheds and potential impact to the health of living beings

Unplanned populational development is the reason of a huge impact in the environment, especially in urban areas. Production of solid waste has been gradually increased and its disposal usually occurs in inappropriate places, as in the headwater of rivers. With respect to water resources, the presence of pollutants results in a significant damage to water ecosystem by turning into an insanitary environment, and harmful to people’s life quality. Such damage refers to sediments, fertilizers, oils, heavy metals, among others, that are usually thrown in different watersheds, mainly in the urban ones.

Upper limits for road salt pollution in lakes

AbstractWidespread and increasing use of road deicing salt is a major driver of increasing lake chloride concentrations, which can negatively impact aquatic organisms and ecosystems. We used a simple model to explore the controls on road salt concentrations and predict equilibrium concentrations in lakes across the contiguous United States. The model suggests that equilibrium salt concentration depends on three quantities: salt application rate, road density, and runoff (precipitation minus evapotranspiration). High application combined with high road density leads to high equilibrium salt concentrations regardless of runoff. Yet if application can be held at current rates or reduced, concentrations in many lakes situated in lightly to moderately urbanized watersheds should equilibrate at levels below currently recommended thresholds. In particular, our model predicts that, given 2010–2015 road salt application rates, equilibrium chloride concentrations in the contiguous United States will exceed the current regulatory chronic exposure threshold of 230 mg L−1 in over 2000 lakes; will exceed 120 mg L−1 in over 9000 lakes; and will be below 120 mg L−1 in hundreds of thousands of lakes. Our analysis helps to contextualize current trends in road salt pollution of lakes, and suggests that stabilization of equilibrium chloride concentrations below thresholds designed to protect aquatic organisms should be an achievable goal.

Leveraging mesh modularization to lower the computational cost of localized updates to regional 2D hydrodynamic model outputs

Hydrodynamic model outputs are used in urban flood risk modelling, flood alert systems, and Monte Carlo hazard assessment. This study tackles an under-explored challenge wherein regular updates to the spatial characteristics of the watershed – due to factors such as changing land use – alter the watershed’s response to rainfall forcing, thus rendering existing model outputs obsolete. Because state-of-the-art hydrodynamic models are computationally expensive, frequently re-running simulations can be costly. Modularization addresses this problem by requiring re-computation only for a limited domain affected by the land use changes. This article introduces a novel approach by modularizing the 2D domain into independent sub-domains before (‘discrete’) and after (‘abstract’) the numerical computations. Using the Hydrologic Engineering Center River Analysis System (HEC-RAS) 2D model of a large urban watershed in Houston as an illustrative and generalizable testbed, we show that both the discrete and abstract modularization closely approximates the results from re-running the entire model. The computational cost of modularization scales linearly with model size for memory requirements as storing the solution on the interior boundaries (discrete) or throughout the domain (abstract) are necessary. This trade-off of memory for computation may facilitate advances in surrogate modelling or Monte Carlo flood risk assessment.

Aerial characterization of surface depressions in urban watersheds

Digital elevation models (DEM) are one of the most fundamental inputs for hydrological modeling. It has been a common practice to remove all surface depressions in a DEM as they are assumed to be data errors. The emerging technology of unmanned aircraft systems (UAS) provides an opportunity to re-examine this assumption at the hyperspatial resolution. This study was the first attempt to characterize small surface depressions in urban environments using UAS imagery. Using an urban area in south Texas as the study site, UAS flights were conducted to yield hybrid DEMs at the resolution of 8–14 cm, coupled with comprehensive ground truth collection. Surface depressions identified from the UAS DEMs were first corrected based on the vertical accuracy of DEMs and then validated through field surveys, with comparisons to two existing LiDAR DEMs (1-m and 10-m). The hydrological impacts of different DEM-derived estimates of catchment depression storage were examined using the Curve Number method across different design storms. Results show that the UAS DEMs outperformed the LiDAR DEMs in describing the microtopographic control of urban overland flow and associated hydrological connectivity across built and natural features. The 8-cm UAS DEM revealed 926% more depression storage than the 10-m LiDAR DEM. This demonstrates a compelling correlation between increasing DEM resolution and enhanced quantification of depression volume. Consequently, the increased depression storage reduced surface runoff by 41% under a two-year design storm and 13% under a 200-year design storm. The results suggest a strong relationship between the DEM resolution and the derived depression estimates, aligning with the fractal nature of watershed systems. Also, the results indicate that the centimeter-level UAS DEMs were not immune from problems. They could yield fake depressions caused by factors such as vegetation, temporary street objects, and underground sewer pipes. The findings of this study suggest the need to quantify the relationships between DEM resolution and associated hydrological attributes and develop new digital drainage analysis algorithms that could effectively incorporate UAS data into urban hydrological modeling.

Chlorophyll-a prediction in tropical reservoirs as a function of hydroclimatic variability and water quality.

The study goal was to determine spatiotemporal variations in chlorophyll-a (Chl-a) concentration using models that combine hydroclimatic and nutrient variables in 150 tropical reservoirs in Brazil. The investigation of seasonal variability indicated that Chl-a varied in response to changes in total nitrogen (TN), total phosphorus (TP), volume (V), and daily precipitation (P). Therefore, an empirical model for Chl-a prediction based on the product of TN, TP, and normalized functions of V and P was proposed, but their individual exponents as well as a general multiplicative factor were adjusted by linear regression for each reservoir. The fitted relationships were capable of representing algal temporal dynamics and blooms, with an average coefficient of determination of R2 = 0.70. The results revealed that nutrients yielded better predictability of Chl-a than hydroclimatic variables. Chl-a blooms presented seasonal and interannual variability, being more frequent in periods of high precipitation and low volume. The equations demonstrate different Chl-a responses to the parameters. In general, Chl-a was positively related to TN and/or TP. However, in some cases (22%), high nutrient concentrations reduced Chl-a, which was attributed to limited phytoplankton growth driven by light deficiency due to increased turbidity. In 49% of the models, precipitation intensified Chl-a levels, which was related to increases in the nutrient concentration from external sources in rural watersheds. Contrastingly, 51% of the reservoirs faced a decrease in Chl-a with precipitation, which can be explained by the opposite effect of dilution of nutrient concentration at the reservoir inlet in urban watersheds. In terms of volume, in 67% of the reservoirs, water level reduction promoted an increase in Chl-a as a response to higher nutrient concentration. In the other cases, Chl-a decreased with lower water levels due to wind-induced destratification of the water column, which potentially decreased the internal nutrient release from bottom sediment. Finally, applying the model to the two largest studied reservoirs showed greater sensitivity of Chl-a to changes in water use classes regarding variations in TN, followed by TP, V, and P.

Accumulation and transport of nutrient and pollutant elements in riparian soils, sediments, and river waters across the Thames River Watershed, Connecticut, USA

Understanding drivers of nutrient and pollutant elements (NPEs) in soils, sediments, and river water is important for protecting water resources and aquatic ecosystems. The objectives of this study were to quantify accumulation and transport of NPEs (P, As, Cd, Cu, Ni, Pb, and Zn) in riparian soils, sediments, river water, and watershed-scale exports within seven post-industrial subwatersheds of the Thames River, Connecticut, USA. Suspended sediments and river water samples were collected from February 2019 to January 2020. Arsenic concentrations in soil (6 to 18 mg kg−1) and sediments (8 to 85 mg kg−1) generally exceeded state and federal EPA quality targets but not river water. Elevated Pb ‘hot spots’ occurred in some riparian soils (>2000 mg kg−1) and sediments (>200 mg kg−1), but the other NPEs concentrations were below toxic thresholds. Riparian soil concentrations and watershed land cover were generally weak predictors for NPE concentrations in bottom sediments, suspended sediments, and river water. DOC, Mn, and Fe concentrations were important predictors for area-normalized dissolved and sediment-bound export of NPEs across the seven watersheds. Dissolved export was greater than sediment export for Mn, P, As, Cd, Cu, and Ni but not for Fe, Pb, and Zn. Watersheds with higher farmland had higher P river water concentrations, but the larger, more urbanized watershed had the highest total and area-normalized P export. An estuarine sediment core that captures sediment from the whole watershed and spans pre-industrial conditions through present shows that export of most NPEs has decreased since its peak, but all remain above baseline throughout the Thames River watershed. Future constraints on surface soil-river exchange and erosion inputs are needed to investigate rates of NPE sourcing to the watersheds.

Evaluating Urban Stream Flooding with Machine Learning, LiDAR, and 3D Modeling

Flooding in urban streams can occur suddenly and cause major environmental and infrastructure destruction. Due to the high amounts of impervious surfaces in urban watersheds, runoff from precipitation events can cause a rapid increase in stream water levels, leading to flooding. With increasing urbanization, it is critical to understand how urban stream channels will respond to precipitation events to prevent catastrophic flooding. This study uses the Prophet time series machine learning algorithm to forecast hourly changes in water level in an urban stream, Hunnicutt Creek, Clemson, South Carolina (SC), USA. Machine learning was highly accurate in predicting changes in water level for five locations along the stream with R2 values greater than 0.9. Yet, it can be challenging to understand how these water level prediction values will translate to water volume in the stream channel. Therefore, this study collected terrestrial Light Detection and Ranging (LiDAR) data for Hunnicutt Creek to model these areas in 3D to illustrate how the predicted changes in water levels correspond to changes in water levels in the stream channel. The predicted water levels were also used to calculate upstream flood volumes to provide further context for how small changes in the water level correspond to changes in the stream channel. Overall, the methodology determined that the areas of Hunnicutt Creek with more urban impacts experience larger rises in stream levels and greater volumes of upstream water during storm events. Together, this innovative methodology combining machine learning, terrestrial LiDAR, 3D modeling, and volume calculations provides new techniques to understand flood-prone areas in urban stream environments.

Advances in ecotechnological methods for diffuse nutrient pollution control: wicked issues in agricultural and urban watersheds

Considerable time and funding have been committed to tackling nonpoint source (NPS) pollution in agricultural and urban watersheds . Notwithstanding all these efforts, the water quality in many AUWs has not significantly improved. Diffuse nutrient pollution involves the movement of these pollutants between soil and water. Excessive diffuse pollution has been accepted as one of the main causes of failure to attain favorable environmental conditions in freshwater systems. Recently, several technologies and practices have been implemented to manage diffuse pollution, namely: a) source reduction, b) pollutant retention over the movement process; c) nutrient recycling, and d) purification and restoration of the eutrophic water bodies. This paper synthesized the existing knowledge of key methods to tackle diffuse pollution from AUWs. Furthermore, the predominant purification mechanisms and impacting factors are explored, allowing a comprehensive and critical understanding of different control strategies to improve the management of diffuse pollution. Therefore, potential approaches for strengthening the performance of control technologies for diffuse pollution treatment and remediation are discussed. Although adopting source reduction strategies (e.g., the “4R” approach: right rate, right time, right source, and right placement of nutrients) could efficiently decrease surface runoff and pollutant levels, they may not stop runoff from entering nearby streams. Consequently, comprehensive treatment of agricultural runoff still requires extra process retention strategies. Overall, the findings of this paper showed that treatment system design and operational and environmental factors played crucial but variable roles in diffuse pollution treatment. Moreover, the results showed that combining or integrating constructed wetlands with other control technologies could enhance the comprehensive purification of diffuse pollution compared to using a single method. This review proposes a systematic approach for diffuse pollution control based on three components (water, soil and microbiota) and maximizing the regulating services of agroecosystems via land use/cover types. The current review contributes to the documentation of existing research trends. It sheds light on diffuse pollution control approaches in AUWs, and further encourages the development of this vital field.

Rainfall-Runoff Modelling Using HEC-HMS Model, Remote Sensing and GIS in Middle Gujarat, India

Hydrological modeling is a widely used approach for estimating the hydrological response of a basin to precipitation. Floods are among the most catastrophic natural disasters in small urban watersheds, inflicting loss of life, massive property destruction, and a severe danger to the economy. As a result, appropriate modeling can be a useful tool in preventing and mitigating such flood hazards. Despite this, flash flood prediction remains one of the challenges of hydrological modeling in ungauged basins due to a lack of runoff observations. This study aims to calibrate and validate the rainfall-runoff transformation model for Hathmati river sub watershed in the Sabarmati River basin using HEC-HMS (Hydrologic Engineering Centre Hydrology Modeling System). For the loss rate, SCS Curve Number method was selected while Clark Unit Hydrograph and SCS unit hydrograph was used for the transform method. The model is calibrated and verified using two rainfall-runoff events from 2006 and 2007 year The model calibration and validation efficiency were verified for both methods using the Nash-Sutcliffe efficiency (NSE), The coefficient of determination (R2), and the Percent Bias (PBIAS) As a result, the model calibration and validation were found to be satisfactory with the acceptable value of NSE between 0.869 to 0.914, with R2 0.901 to 0.947 and PBIAS from 9.76 to 14.8. it is observed that the model shows a very good correlation between simulated flow and observed flow. As a result, the model can be used to forecast river flow and aid in flood mitigation efforts to lessen their effects and associated costs. Additionally, the findings of this study can serve as guidelines for future assessments of the flood risk in the study area.

Evolution of gully erosion and susceptibility factors in the urban watershed of the Kimemi (Butembo/DR Congo)

Gully erosion is one of the most intense landscape degradation mechanisms in areas with varying environmental characteristics. Both natural and anthropogenic factors affect the gullying process. Reliable documentation of these processes in tropical African cities is scarce. This study assessed the gully erosion dynamic and the susceptibility factors in the urban watershed of Kimemi in eastern Democratic Republic of Congo (DRC). Data were obtained through a combination of fieldwork and digitization of very high spatial resolution images from Google Earth (from 2011 to 2021). The length, width, and area of large gullies (width ≥ 5 m) were measured for each year of the study. A logistic regression model (LRM) was also used to investigate the influence of both physical and anthropogenic factors on gully susceptibility. The results revealed that the number of gullies has increased from 36 to 61 during the last decade. The gully mean length of 63.9 ± 61.1 m, 129.3 ± 104.9 m, and 174.7 ± 153.8 m were obtained for the years 2011, 2015, and 2021 respectively. The average density of gully network for the study period was 0.12 km/km², while the degraded land was ∼1.3 and ∼1.1 ha/year for 2011–2015 and 2015–2021 for the entire watershed. The significant changes in morphometric parameters (length, width, area) were found only in the bare land and building land uses. A strong and positive relationship between the length (m) and the area (ha) was found. Furthermore, the susceptibility of gullying was significantly influenced by the slope, stream power index (SPI), distance to roads and rivers, land use and land cover (LULC), and normalized difference vegetation index (NDVI). This means the areas located in the bare land and building or close to roads and/or streams are more likely to be gullied. The findings emphasize the impact of urbanization on gully erosion in the Kimemi watershed, highlighting the importance of informed land management decisions with a close attention to anthropogenic factors.

Spatial variation of periphytic desmid community structure on emergent macrophytes in a tropical urban watershed

Spatial variation of periphytic desmid community structure on emergent macrophytes in a tropical urban watershed

Sewer subsidies from overflows and pipe leaks dominate urban stream solute loads in all storm events

Stream channel burial drastically alters watershed flowpaths by routing surface waters underground and increasing the potential for interactions between stream water and urban infrastructure such as storm and sanitary sewers. While numerous studies have investigated storm event solute loads from urban watersheds, the influences of stream channel burial and sewer overflows are often overlooked. This study uses grab samples and natural abundance stable isotope tracers to quantify the event dynamics of solute concentration-discharge relationships as well as cumulative loads in a buried urban stream. Our results demonstrate that different solutes, as well as different sources of the same solute (atmospheric NO3− and sewer-derived NO3− differentiated by the Δ17O tracer), are delivered via separate watershed flowpaths and thus have different timings within the event and contrasting relationships to flow. This inter-event variability reveals dynamics that result from temporal and spatial heterogeneity in infiltration, exfiltration, and pipe overflows. These results can help guide system-wide infrastructure maintenance as cities seek to meet challenges in sustaining and improving water quality as infrastructural systems age.

Monitoring spore washoff during a biological contamination incident response using automated stormwater samplers and sensors to predict contamination movement

This study examined the washoff of Bacillus globigii (Bg) spores from concrete, asphalt, and grass surfaces by stormwater. Bg is a nonpathogenic surrogate for Bacillus anthracis, which is a biological select agent. Areas (2.74 m × 7.62 m) of concrete, grass, and asphalt were inoculated twice at the field site during the study. Spore concentrations were measured in runoff water after seven rainfall events (1.2–65.4 mm) and complimentary watershed data were collected for soil moisture, depth of water in collection troughs, and rainfall using custom-built telemetry units. An average surface loading of 107.79 Bg spores/m2 resulted in peak spore concentrations in runoff water of 102, 260, and 4.1 CFU/mL from asphalt, concrete, and grass surfaces, respectively. Spore concentrations in the stormwater runoff were greatly reduced by the third rain event after both inoculations, but still detectable in some samples. When initial rainfall events occurred longer after the initial inoculation, the spore concentrations (both peak and average) in the runoff were diminished. The study also compared rainfall data from 4 tipping bucket rain gauges and a laser disdrometer and found they performed similarly for values of total rainfall accumulation while the laser disdrometer provided additional information (total storm kinetic energy) useful in comparing the seven different rain events. The soil moisture probes are recommended for assistance in predicting when to sample sites with intermittent runoff. Sampling trough level readings were critical to understanding the dilution factor of the storm event and the age of the sample collected. Collectively the spore and watershed data are useful for emergency responders faced with remediation decisions after a biological agent incident as the results provide insight into what equipment to deploy and that spores may persist in runoff water at quantifiable levels for months. The spore measurements are also a novel dataset for stormwater model parameterization for biological contamination of urban watersheds.

Optimization land use based on multi-scenario simulation of ecosystem service for sustainable landscape planning in a mixed urban - Forest watershed

Integrating ecosystem services (ESs) into land development strategies can provide a new perspective in order to make more informed land use (LULC) decisions. In this sense, a specific framework is provided to use ESs in land allocation in Ilam urban watershed, Western Iran. This region is experiencing unsustainable development and destruction of natural ecosystems and as a result, these conditions have affected ecological characteristics, and ESs. Therefore, characterizing the LULC of this watershed and its impact on ESs is significant to comprehensively understanding the influences of human activities on ecosystems. Hence, the simulated annealing-genetic hybrid algorithm was assessed to optimize LULC using Six types of ESs; including, food provisioning (FP), water yield (WY), sediment retention (SR), recreation quality (RQ), aesthetic quality (AQ) and habitat quality (HQ). Regarding optimization approach, FP, WY, SR, RQ, AQ, HQ and land integration (LI) scenarios were designed based on LULC types and ESs. Considering the land allocation, the results indicated that most changes are related to the northwest, southeast, southwest and middle parts of the region. Moreover, an increasing trend was observed regarding dense forest and low-dense forest, according to the following scenarios: FP, RQ, LI, AQ, WY, SR and HQ. In contrast, a decreasing trend was obtained for cropland in the same order of scenarios. Additionally, the highest areas of garden, grassland, park, river, urban land, and road classes were observed in scenarios HQ, LI, SR, WY and FP, respectively. The results also revealed that the SDR scenario can be regarded as the best one having the lowest LULC fragmentation. Our study indicated that using ESs to optimize LULC allocation is a useful and an important strategy due to the fact that one can consider both the function and the structure of ecosystems in LULC planning and management decisions. Thus, the results of this research can help land managers in order to develop LULC, based on ESs and ecological conditions, which would finally lead to maintain the ESs and achieve sustainable development.

Total suspended solids loading of stormwater from different land use areas in an urban watershed

Purpose. Land use within a watershed affects surface water quality by creating a process by which diffuse pollutants such as suspended solids, trace metals, and nutrients enter rivers and streams. The purpose of this study is to assess pollution-load for Total Suspended Solids (TSS) and some trace metals in runoff samples collected during storm events in selected sub-catchment locations representing different land use areas in an urban watershed; and to determine the effects of land-use on the content of pollutants in stormwater using Event Mean Concentration (EMC).&#x0D; Results. There were high EMC and Site Mean Concentrations (SMC) of TSS in stormwater in the six land-use zones examined, with values ranging from 154.0 mg L−1 to 1464.0 mg L−1; and 216.5 mg L−1 to 1153.4 mg L−1 for EMC and SMC respectively. The total content of suspended solids was significantly high, above the acceptable threshold of 100.0 mg L−1 stipulated by the WHO. The researchers also found a statistically significant variation in TSS loading of stormwater from the commercial land-use areas compared with the other land-use zones. A strong correlation was also observed between the volume of stormwater discharged and the TSS load. However, the concentrations of trace metals in stormwater were low across the land use zones. The commercial districts of the studied cities were found to be major sources of suspended solids in stormwater, and pollution of the urban watersheds leading to the deterioration of the rivers.&#x0D; Scientific novelty. This study attempted to qauntify TSS load in stormwater and determine the contributions of the diffferent urban land-use areas to pollution yield.. It contributes to scientific efforts to directly quantify surface water pollution from nonpoint sources, since little attention has been paid to diffuse pollution, especially in sub-Saharan Africa; and provides baseline data for assessing urban stormwater in low-income countries.&#x0D; Practical value. This study offers guidelines for city authorities to develop land use policies to control surface water pollution and urban waste. The findings may also serve as emperical basis for greater advocacy by civil society organizations for the proper management and control of urban rivers and streams for public health benefits.

Downpour dynamics: outsized impacts of storm events on unprocessed atmospheric nitrate export in an urban watershed

Abstract. Water quality impacts of stream water nitrate (NO3-) on downstream ecosystems are largely determined by the load of NO3- from the watershed to surface waters. The largest NO3- loads often occur during storm events, but it is unclear how loads of different NO3- sources change during storm events relative to baseflow or how watershed attributes might affect source export. To assess the role of storm flow and baseflow in NO3- source export and how these roles are modulated by hydrologic effects of land-use practices, we measured nitrogen (δ15N) and oxygen (Δ17O) isotopes of NO3- and oxygen isotopes (δ18O) of water in rainfall and stream water samples from before, during, and after eight storm events across 14 months in two Chesapeake Bay watersheds of contrasting land use. Storms had a disproportionately large influence on the export of unprocessed atmospheric NO3- (NO3Atm-) and a disproportionately small influence on the export of terrestrial NO3- (NO3Terr-) relative to baseflow in the developed urban watershed. In contrast, baseflow and storm flow had similar influences on NO3Atm- and NO3Terr- export in the mixed agricultural–forested watershed. An equivalent relationship between NO3Atm- deposition on impervious surfaces and event NO3Atm- stream water export in the urban watershed suggests that impervious surfaces that hydrologically connect runoff to channels likely facilitate the export of NO3Atm- during rainfall events. Additionally, larger rainfall events were more effective at exporting NO3Atm- in the urban watershed, with increased rainfall depth resulting in a greater fraction of event NO3Atm- deposition exported. Considering both projected increases in precipitation amounts and intensity and urban/suburban sprawl in many regions of the world, best management practices that reduce the hydrologic connectivity of impervious surfaces will likely help to mitigate the impact of storm events on NO3Atm- export from developed watersheds.