Micro and Macroscale Drivers of Nutrient Concentrations in Urban Streams in South, Central and North America (original) (raw)
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Freshwater Science, 2019
Studies of the effects of landscape configuration on nutrient concentrations in aquatic systems, apart from land cover percentages, remain limited. Understanding these influences is important to guide land use planning and avoid the undesirable consequences of artificial eutrophication. We investigated how land use and natural landscape attributes such as edge density, mean shape index, cohesion, and contagion were related to nitrate (N-NO 3) and phosphate (P-PO 4) concentrations in Brazilian streams and Mexican lakes. Data on nutrient concentrations were collected by citizen science volunteers from 2013 to 2016, and we calculated land use classes and landscape metrics for each watershed. We developed models to predict nutrient concentrations based on landscape metrics, watershed slope, and season after excluding autocorrelated predictors. We used the Generalized Additive Model for Location, Shape and Scale framework and found the distribution (gamma or lognormal) that provided the best fit to the data based on the Akaike Information Criterion. The best predictors were selected following a stepwise strategy. We found relatively high N-NO 3 (5-10 mg/L) and P-PO 4 (0.5-1.0 mg/L) concentrations in the watersheds in both countries. Landscape composition (percentages of urban and agricultural areas) and configuration (mean shape indexes for urban and agricultural land use) metrics were the key predictors in the model for P-PO 4 in Brazilian streams. In Mexican lakes, the predictors of nutrient concentrations were configuration metrics such as contagion and edge density of natural areas for P-PO 4 , and cohesion of urban areas for N-NO 3. Our findings can be used as a starting point for land use planning, as well as for helping managers predict nutrient enrichment in watersheds within existing urban and agricultural areas. Our study highlights the importance of community-based monitoring that supplements regular monitoring initiatives because we were able to use data collected by citizen scientists to assess potential drivers of nutrient pollution and differences between countries.
Knowing reference (i.e., baseline) riverine nutrient concentrations is essential to understand fundamental processes of biogeochemical transport from continents to the ocean, describing ecological conditions, and informing managers of best attainable conditions for nutrient abatement and controlling anthropogenic eutrophication. We used data from 434 Brazilian watersheds representative of six South American biomes to estimate expected nutrient levels in the absence of anthropogenic influence. We used a novel watershed-based approach to describe spatial patterns throughout Brazil and for the entire Amazon basin. We found reference total nitrogen concentrations were most closely related to biome, whereas total phosphorus levels were to soil properties in addition to climatic factors influencing biomes. We found that many areas have intrinsically high background phosphorus and relatively low nitrogen, suggesting nitrogen-limitation of freshwaters could be widespread in South America, a...
Biogeochemistry, 2000
This study documents regional patterns in stream nitrogen and phosphorus concentrations in the Brazilian state of Rondônia in the southwestern Amazon basin, and interprets the patterns as functions of watershed soil properties, deforestation extent, and urban population density. The survey includes 77 different locations sampled in the dry and wet seasons, with a watershed size range from 1.8 to 33,000 km 2 over a total area of approximately 140,000 km 2 . A sequential regression technique is used to separate the effects of natural watersheds properties and anthropogenic disturbance on nutrients and chloride. Natural variation in soil texture explains most of the variance in stream nitrate concentrations, while deforestation extent and urban population density explain most of the variance in stream chloride (Cl) and total dissolved nitrogen (TDN) concentrations. Stream TDN, total dissolved phosphorus (TDP), particulate phosphorus (PP) and Cl concentrations all increase non-linearly with deforestation extent in the dry season after controlling for natural variability due to soil type. Stream nutrient and Cl disturbances are observed only in watersheds more than 66-75% deforested (watershed area range 2-300 km 2 ), suggesting stream nutrient concentrations are resistant to perturbation from vegetation conversion below a 66-75% threshold. In heavily deforested watersheds, stream Cl shows the largest changes in concentration (12 AE 6 times forested background), followed by TDP (2.3 AE 1.5), PP (1.9 AE 0.8) and TDN (1.7 AE 0.5). Wet season signals in Cl and TDP are diluted relative to the dry season, and no land use signal is observed in wet season TDN, PN, or PP. Stream TDN and TDP concentrations in non-urban watersheds both correlate with stream Cl, suggesting that sources other than vegetation and soil organic matter contribute to enhanced nutrient concentrations. Small, urbanized watersheds (5-20 km 2 ) have up to 40 times the chloride and 10 times the TDN concentrations of forested catchments in the dry season. Several large watersheds (*1000-3000 km 2 ) with urban populations show higher Cl, TDN and TDP levels than any small pasture watershed, suggesting that human impacts on nutrient concentrations in large river systems may be dominated by urban areas. Anthropogenic disturbance of dry-season stream Cl and TDN is detectable in large streams draining deforested and urbanized watersheds up to 33,000 km 2 . We conclude that regional deforestation and urbanization result in changes in stream Cl, N and P concentrations at wide range of scales, from small pasture streams to large river systems.
2001
The Parque Estadual Turistico do Alto Ribeira (PETAR) is an Atlantic rain forest reserve in South-eastern Brazil. A few small villages are located inside the watersheds of the three main rivers that cross the park, Betari, Iporanga and Piloes. Untreated domestic sewage from households is often discharged directly into the watercourses. Subsistence agriculture is practiced by most of those families, which adds nutrients to the stream due to increased soil erosion. Additionally, larger farms located near the headwater of PETAR rivers use fertilizers to improve soil condition. The main goal of this study is to investigate seasonal and spatial variability in nutrient concentration in PETAR watercourses due to inputs from human settlements and agricultural areas within or near the park. Twenty-one sites located in fifteen streams were surveyed during field campaigns carried on in June and November 1998. Nitrogen and phosphorus concentration, as well as other physical and chemical water p...
Biogeochemistry, 2013
The influence of built urban infrastructure on stream chemistry was quantified throughout the drainage network of the tropical Río Piedras watershed, San Juan metropolitan area, Puerto Rico. Urbanization and failing domestic wastewater infrastructure appeared to drive changes in surface water chemistry throughout the watershed. Mean baseflow concentrations of chloride (Cl), ammonium (NH 4), dissolved organic carbon (DOC), dissolved organic nitrogen (DON), and phosphate (PO 4) all increased with urban infrastructure, while nitrate (NO 3) and dissolved oxygen (DO) decreased. These patterns in stream chemistry suggest that sewage effluent from failing or illegally connected sewer pipes has a major impact on surface water quality. Concentrations of Cl, DO, and NH 4 in stream water were most strongly related to sewer pipe volume, demonstrating the tight connection between urban infrastructure and stream chemistry. The loading and transformation of NO 3 and NH 4 were modeled along the river network and NH 4 loading rates from the landscape were strongly related to urban infrastructure, whereas NO 3 loading rates showed only weak relationships, highlighting the importance for incorporating NH 4 dynamics into river network models in urban environments. Water quality appears to be severely impacted by sewage in this tropical basin, despite large investments in built infrastructure. The high temperatures in the Río Piedras exacerbate water quality problems by reducing saturation DO levels in streams, and intense rainstorms tax the ability of built infrastructure to adequately manage overland flows. These problems are likely typical of much of the urbanized humid tropics.
Environmental monitoring and assessment, 2017
Freshwater resources are increasingly scarce due to human activities, and the understanding of water quality variations at different spatial and temporal scales is necessary for adequate management. Here, we analyze the hypotheses that (1) the presence of a wastewater treatment plant (WWTP) and (2) a polluted tributary that drains downstream from the WWTP change the spatial patterns of physicochemical variables (pH, turbidity, dissolved oxygen, and electrical conductivity) and nutrient concentrations (reactive soluble phosphorus, total phosphorus, nitrogen series, total nitrogen, and total dissolved carbon) along a mid-order river in SE Brazil and that these effects depend on rainfall regime. Six study sites were sampled along almost 4 years to evaluate the impacts of human activities, including sites upstream (1-3) and downstream (5-6) from the WWTP. The impacts were observed presenting an increasing trend from the source (site 1) towards Água Quente stream (site 4, the polluted tr...
Environmental Management, 2011
Determining reference concentrations in rivers and streams is an important tool for environmental management. Reference conditions for eutrophication-related water variables are unavailable for Brazilian freshwaters. We aimed to establish reference baselines for São Paulo State tropical rivers and streams for total phosphorus (TP) and nitrogen (TN), nitrogen-ammonia (NH 4 ? ) and Biochemical Oxygen Demand (BOD) through the best professional judgment and the trisection methods. Data from 319 sites monitored by the São Paulo State Environmental Company (2005 to 2009) and from the 22 Water Resources Management Units in São Paulo State were assessed (N = 27,131). We verified that data from different management units dominated by similar land cover could be analyzed together (Analysis of Variance, P = 0.504). Cumulative frequency diagrams showed that industrialized management units were characterized by the worst water quality (e.g. average TP of 0.51 mg/L), followed by agricultural watersheds. TN and NH 4 ? were associated with urban percentages and population density (Spearman Rank Correlation Test, P \ 0.05). Best professional judgment and trisection (median of lower third of all sites) methods for determining reference concentrations showed agreement: 0.03 & 0.04 mg/L (TP), 0.31 & 0.34 mg/L (TN), 0.06 & 0.10 mg-N/L (NH 4 ? ) and 2 & 2 mg/L (BOD), respectively. Our reference concentrations were similar to TP and TN reference values proposed for temperate water bodies. These baselines can help with water management in São Paulo State, as well as providing some of the first such information for tropical ecosystems.
Non-Point-Source Impacts on Stream Nutrient Concentrations Along a Forest to Urban Gradient
Environmental Management, 2005
We conducted statistical analyses of a 10year record of stream nutrient and sediment concentrations for 17 streams in the greater Seattle region to de-termine the impact of urban non-point-source pollutants on stream water quality. These catchments are dominated by either urban (22-87%) or forest (6-73%) land cover, with no major nutrient point sources. Stream water phosphorus concentrations were moderately strongly (r 2 = 0.58) correlated with catchment land-cover type, whereas nitrogen concentrations were weakly (r 2 = 0.19) and nonsignificantly (at a < 0.05) correlated with land cover. The most urban streams had, on average, 95% higher total phosphorus (TP) and 122% higher soluble reactive phosphorus (SRP) and 71% higher turbidity than the most forested streams. Nitrate (NO 3 ), ammonium (NH 4 ), and total suspended solids (TSS) concentrations did not vary significantly with land cover. These results suggest that urbanization markedly increased stream phosphorus concentrations and modestly increased nitrogen concentrations. However, nutrient concentrations in Seattle region urban streams are significantly less than those previously reported for agricultural area streams.
Ecohydrology, 2019
Agricultural activities can affect the delivery of nutrients to streams, riparian canopy cover, and the capacity of aquatic systems to process nutrients and sediments. There are few measures of nutrient uptake and metabolism from tropical or subtropical streams in general, and even fewer from tropical regions of South America. We examined ammonium (NH4 +) and soluble reactive phosphorus (SRP) retention in streams in Brazil and Argentina. We selected twelve streams with relatively little or extensive agricultural activity and conducted whole-stream nutrient additions and measurements of Gross Primary Production (GPP) and Ecosystem Respiration (ER). We used multiple linear regression to determine potential drivers of nutrient uptake metrics across the streams. Nutrient concentrations and retention differed significantly between land use categories. Both NH4 + and SRP concentrations were higher in the agricultural sites (means of 161 and 495 µg L-1 , respectively), whereas metabolic rates were slower and transient storage smaller. Our analysis indicated that agriculture increased ambient uptake lengths and decreased uptake velocities. The regression models revealed that ambient SRP had a positive effect on NH4 + uptake and vice-versa, suggesting strong stoichiometric controls. Drivers for nutrient uptake in streams with low-intensity agriculture also included canopy cover, temperature, and ER rates. Nutrient assimilation in agricultural sites was influenced by a higher number of variables (GPP for SRP, and discharge, and transient storage for both nutrients). Our results indicate agricultural activity changes both the magnitude of in-stream nutrient uptake and the mechanisms that control its variation, with important implications for South American streams under agricultural intensification.