Stormwater Runoff Quality and Quantity from Small Watersheds in Austin, TX: Updated through 2008

This report contains a variety of water quality data from several Waller Creek locations.EXECUTIVE SUMMARY: Almost all stormwater quality activities rely upon monitoring as their foundation to one degree or another. Design and construction of water quality controls or other best management practices (BMPs) are, or should be, based on monitoring data to ensure the BMP meets the desired goals. Rules and regulations that are not based on monitoring data may reflect the desire of the rule maker more than the science of the physical world. Modeling, which may be used to develop rules and design guidelines, is dependent on monitoring to first develop the stochastic or physical theories on which the model is based and then to calibrate the model for a specific location. The City of Austin (COA) engages in all of the above activities; proposing and enforcing development rules and regulation, developing design guidelines for and construction of BMPs, and modeling small and large watersheds. These activities are all based on a solid foundation of stormwater monitoring that has encompassed more than twenty-five years. The City participated in the Nationwide Urban Runoff Program (NURP) in 1981 (Engineering Science and COA, 1983) and included monitoring of two water quality control systems in their 1983-84 cooperative monitoring program agreement with the U.S. Geological Survey (USGS). These two monitoring projects were limited in both scope and duration (COA, 1984; USGS, 1987). In the mid-1980s, COA initiated a more comprehensive monitoring program to collect data to support a series of watershed management ordinances adopted by the City (COA, 1985). The original plan was to monitor eleven sites including seven water quality controls over a five-year period. The longer monitoring period was supposed to allow for monitoring that better reflected the local rainfall and runoff patterns since the earlier programs focused mainly on smaller events. The data from this program were the basis for much of the quality and quantity information in the current COA Environmental Criteria Manual (ECM) as well as initial discussions on the first-flush phenomena and design criteria for the Austin sand filter design. In 1990 COA started a comprehensive monitoring program to meet the City's ongoing stormwater monitoring needs (COA, 1996). These needs include evaluating the design and iii performance of different types of structural BMPs, evaluating effectiveness of education programs, evaluating and refining quality and quantity of runoff from different types of land use and meeting the requirements of the City's MS4 discharge permit under the National Pollution Discharge Elimination System (NPDES) and Texas Pollution Discharge Elimination System (TPDES) portions of the Clean Water Act. Through 2008, the Stormwater Quality Evaluation (SQE) Section of the Watershed Protection Department has collected runoff quality and quantity data from more than one hundred monitoring locations including twenty-eight BMPs and ten watersheds greater than five hundred acres. This report is intended to summarize the runoff quality and quantity data collected by the city of since 1981. During the preceding thirty years collection techniques, equipment and personnel have changed, all having an impact on data quality. However, the data used in this report represent a unique dataset in both scope and duration. While far from an exhaustive examination of the data, this report does verify some existing hypotheses and also challenges some existing assumptions. The relationship between total impervious cover (TIC) and Rv found in this report differs significantly from that found in the COA ECM (2009). If the relationship found in this report is adopted there will be no changes in capture volume requirements for BMPs currently found in the COA ECM except wet ponds which would be larger for most cases. There could be impacts on the designs for alternative controls as well. An earlier COA study (2006) found no difference between the runoff from recharge and non-recharge areas, so only one relationship is presented here. It was demonstrated that some mean pollutant concentrations changed with development conditions. Ammonia (NH3), lead (Pb) and zinc (Zn) increased exponentially with impervious cover. Total phosphorus (TP), dissolved phosphorus (DP), total Kjeldahl nitrogen (TKN) and total nitrogen (TN) increased as the fraction of non-urban land decreased. Chemical oxygen demand (COD), 5-day biochemical oxygen demand (BOD), cadmium (Cd) and copper (Cu) increased linearly as total impervious cover increased. Fecal coliform (FCOL) increased as the fraction of single-family residential (SFR) land use increased while volatile suspended solids (VSS) varied with changes in SFR and commercial land uses. Nitrate + nitrite (NO3+NO2) iv concentrations were different between developed and undeveloped areas but there were no significant relationships with impervious cover or land use. Fecal streptococci (FSTR), total organic carbon (TOC) and total suspended solids (TSS) were not significantly related to any changes in development condition tested in this report. A table was prepared to replace the existing COA ECM (2009) stormwater concentration assumption in Tables 1.10 and 1.11. This change would have no impact on existing BMP designs but would impact the design of alternative controls. It was found that using disconnected impervious area (DCIA) instead of TIC did not result in improved predictions of mean concentrations or runoff-rainfall ratios, Rv. DCIA was estimated in this report based on empirical relationships developed elsewhere. If local relationships are developed or if DCIA were actually measured, this conclusion may be different. Significant relationships were developed to predict event mean concentrations (EMCs) for the pollutants studied and four classes of development. The models used one or more of the following as predictive variables: preceding dry time, 15-minute peak rainfall intensity and total rainfall. While these models were statistically significant, most models resulted in predictions that were no better than using the mean of the observed values. Better physical models are needed to predict EMCs, rather than relying on stochastic relationships. The analyses confirmed results of earlier studies that indicated runoff concentrations are not constant during a runoff event in small watersheds with moderate to high impervious cover. The first-flush effect was less pronounced (even non-existent for some pollutants) in undeveloped areas. While other studies focused solely on impervious cover, this report also examined the type of land use associated with the impervious cover. It was found that in SFR areas, nutrients, especially dissolved nutrients, exhibited a last-flush with pollutant concentrations increasing rather than decreasing as runoff volume increased. This effect may have a substantial impact future BMP design. Testing of proposed modifications to the NRCS curve number method found a slight improvement over the currently accepted method but it still under predicts runoff volumes for v smaller events: those of most concern for water quality design. While the curve number method may still be used for flood design, models based on physical processes should be employed when attempting to perform continuous simulations for water quality design.Waller Creek Working Grou

Nitrogen transport and retention dynamics across central European catchments using large-sample data

Human activities, especially agricultural practices, have significantly altered the Earth’s landscape and the global cycle of nitrogen. In Europe, diffuse nitrogen (N) input from agriculture has been identified as a major driver of marine eutrophication. Despite a long history of measures, little improvement in groundwater and surface water quality has been observed. Recent studies have attempted to provide insights into nitrogen dynamics at the catchment scale, helping to explain the causes and effects of persistent water quality problems. However, there is a lack of large-scale, long-term studies that provide insights into both biogeochemical and hydrological N legacies under different landscape settings. Here using data of more than 100 German catchments of the last seven decades, we synthesis the nitrogen transport and retention dynamics, as well as their dominant (landscape and climate) controls in a large-sample setting. To this end, we adapted the mHM-SAS model (Nguyen et al., 2021) to reflect regional-scale biogeochemical and hydrological N legacies, taking into account the historical development of both diffuse and point sources. The underlying parameterizations were constrained using instream N concentrations. We found high heterogeneity in catchment responses to N inputs. The fractions of N surplus that were stored in the soil, removed by denitrification, stored in the subsurface, and finally exported to the stream vary over a wide range. Our analysis of the long-term (1950-2014) average N balances from all catchments suggests that a majority (mean = 57%) of N surplus was removed by denitrification, followed by stream N export (27%) and the rest was stored in the catchment (16%). Despite the reduction in N surplus after 1990s, biogeochemical legacy reflected in the soil N build-up showed an increasing trend over the analyzed period (1950-2014) across a majority of the study catchments. As for the hydrologic legacy, we found a varying range of mean transit times of discharge between 3.5 years and 13.1 years (95% confidence interval) among the analyzed catchments. Overall, our large-sample analysis provides a detailed overview of biogeochemical and hydrological N legacies across Germany; and thus provides useful insights for an improvement of agricultural practices and water quality management in Central European landscapes

Droughts can reduce the nitrogen retention capacity of catchments

In 2018–2019, Central Europe experienced an unprecedented multi-year drought with severe impacts on society and ecosystems. In this study, we analyzed the impact of this drought on water quality by comparing long-term (1997-2017) nitrate export with 2018–2019 export in a heterogeneous mesoscale catchment. We combined data-driven analysis with process-based modelling to analyze nitrogen retention and the underlying mechanisms in the soils and during subsurface transport. We found a drought-induced shift in concentration-discharge relationships, reflecting exceptionally low riverine nitrate concentrations during dry periods and exceptionally high concentrations during subsequent wet periods. Nitrate loads were up to 70% higher compared to the long-term load-discharge relationship. Model simulations confirmed that this increase was driven by decreased denitrification and plant uptake and subsequent flushing of accumulated nitrogen during rewetting. Fast transit times (20 years) inhibited a fast response but potentially contribute to a long-term drought legacy. Overall, our study reveals that severe multi-year droughts, which are predicted to become more frequent across Europe, can reduce the nitrogen retention capacity of catchments, thereby intensifying nitrate pollution and threatening water quality

Nitrate and Water Isotopes as Tools to Resolve Nitrate Travel Times in a Mixed Land Use Catchment

For the sake of food production, nutrients like nitrogen (N) are applied on agricultural land to supply crops. However, due to common agricultural practice, the amount of N provided very often significantly exceeds the uptake potential of the plants resulting in a N surplus that accumulates in the soil. Organic soil nitrogen is slowly transformed to nitrate, which is then mobilized by water and moves through the subsurface, with the risk of contaminating receiving water bodies. High nitrate loads cause poor chemical states for 27% of all groundwater bodies in Germany and foster eutrophication in lakes and rivers and by this a loss of biodiversity. The main problem are legacy issues of nitrate pollution, because there is a time lag between N input and nitrate mobilization and transport. Research on nitrate travel times is highly relevant for a reliable prediction of the capability of catchments to store, buffer and release nitrate. However, it is not clear how long nitrate is stored and transported in catchment’s storage. For this study, a 11 km2 headwater catchment with mixed land use within the Northern lowlands of the Harz mountains in Germany was investigated from spring 2017 until the end of 2020. A monitoring program was set up, starting with biweekly samples for the first two years and daily samples for the remainder, with sub-daily samples during precipitation events. Samples were taken from stream water and when available from precipitation water. Nitrate concentrations as well as isotopic signatures of water (δ18O and δ2H) and nitrate (δ18O and δ15N) were analysed. To investigate nitrate travel times, the numerical model tran-SAS (Benettin and Bertuzzo, 2018) was set up und modified for this catchment. Here, a time-variant power law function was used as rank StorAge Selection (SAS) function to select the composition of fluxes considering their age. Nitrate with a distinct δ18O from water, formed during microbial activities in the upper soil zone is transported with leaching water into the subsurface storage where denitrification with the corresponding isotope fractionation occurs. The combination of stable isotopes of water and biogeochemical equations to describe the forming of nitrate isotopes and the fractionation of nitrate isotopes during denitrification, which depends on transit times is a novel tool to investigate nitrate age and nitrate transport. Together with the usage of a SAS-based transit time model to simulate nitrate transport and denitrification in the subsurface, tran-SAS is transformed into a simplified reactive transport model (RTM). A decoupling between nitrate age and water age as well as between nitrate travel times and water travel times is expected. Especially during precipitation events catchment’s processes and travel times are changing due to altering hydrological conditions. The model allows to investigate the age of water and nitrate during different hydrological conditions. This will become more and more important considering more frequent hydrological extremes (droughts and floods) and associated N mobilization in agricultural catchments

QUADICA: Water quality, discharge and catchment attributes for large-sample studies in Germany

Environmental data are the key to define and address water quality and quantity challenges at catchment scale. Here, we present the first large-sample water quality data set for 1386 German catchments covering a large range of hydroclimatic, topographic, geologic, land use and anthropogenic settings. QUADICA (water QUAlity, DIscharge and Catchment Attributes for large-sample studies in Germany) combines water quality with water quantity data, meteorological and nutrient forcing data, and catchment attributes. The data set comprises time series of riverine macronutrient concentrations (species of nitrogen, phosphorus and organic carbon) and diffuse nitrogen forcing data at catchment scale (nitrogen surplus, atmospheric deposition and fixation). Time series are generally aggregated to an annual basis; however, for 140 stations with long-term water quality and quantity data (more than 20 years), we additionally present monthly median discharge and nutrient concentrations, flow-normalized concentrations and corresponding mean fluxes as outputs from weighted regressions on time, discharge, and season (WRTDS). The catchment attributes include catchment nutrient inputs from point and diffuse sources and characteristics from topography, climate, land cover, lithology and soils. This comprehensive, freely available data collection can facilitate large-sample data-driven water quality assessments at catchment scale as well as mechanistic modeling studies

QUADICA: A large-sample data set of water quality, discharge and catchment attributes for Germany

Environmental data are critical for understanding and managing ecosystems, including mitigation of degraded water quality. Therefore, we provide the first large-sample water quality data set of riverine water quality combined with water quantity, meteorological and nutrient forcing data, and catchment attributes for Germany in a preprocessed and structured form. The QUADICA data set (water QUAlity, DIscharge and Catchment Attributes for large-sample studies in Germany) covers 1386 German and transboundary catchments with a large range of hydroclimatic, topographic, geologic, land use and anthropogenic settings. The data set comprises time series of riverine macronutrient concentrations (species of nitrogen, phosphorus and organic carbon), discharge, meteorological and diffuse nitrogen forcing data (nitrogen surplus, atmospheric deposition and fixation). The time series are generally aggregated to an annual basis; however, for 140 stations with long-term water quality and quantity data (more than 20 years), we additionally provide monthly median discharge and nutrient concentrations, flow-normalized concentrations and corresponding mean fluxes as outputs from weighted regressions on time, discharge, and season (WRTDS). The catchment attributes include catchment nutrient inputs from point and diffuse sources and characteristics from topography, hydroclimate, land cover, lithology and soils. QUADICA is a comprehensive, freely available, ready-to-use data set that facilitates large-sample data-driven water quality assessments at catchment scale as well as mechanistic modeling studies. We hope to stimulate the hydrological and water quality communities to provide similar data sets to create novel research opportunities, increase our understanding of catchment functioning, and ultimately improve water quality management

Historical atmospheric pollution trends in Southeast Asia inferred from lake sediment records

Fossil fuel combustion leads to increased levels of air pollution, which negatively affects human health as well as the environment. Documented data for Southeast Asia (SEA) show a strong increase in fossil fuel consumption since 1980, but information on coal and oil combustion before 1980 is not widely available. Spheroidal carbonaceous particles (SCPs) and heavy metals, such as mercury (Hg), are emitted as by-products of fossil fuel combustion and may accumulate in sediments following atmospheric fallout. Here we use sediment SCP and Hg records from several freshwater lentic ecosystems in SEA (Malaysia, Philippines, Singapore) to reconstruct long-term, region-wide variations in levels of these two key atmospheric pollution indicators. The age-depth models of Philippine sediment cores do not reach back far enough to date first SCP presence, but single SCP occurrences are first observed between 1925 and 1950 for a Malaysian site. Increasing SCP flux is observed at our sites from 1960 onward, although individual sites show minor differences in trends. SCP fluxes show a general decline after 2000 at each of our study sites. While the records show broadly similar temporal trends across SEA, absolute SCP fluxes differ between sites, with a record from Malaysia showing SCP fluxes that are two orders of magnitude lower than records from the Philippines. Similar trends in records from China and Japan represent the emergence of atmospheric pollution as a broadly-based inter-region environmental problem during the 20th century. Hg fluxes were relatively stable from the second half of the 20th century onward. As catchment soils are also contaminated with atmospheric Hg, future soil erosion can be expected to lead to enhanced Hg flux into surface waters