Watershed Metrics Research Articles

Developing DNA-Based Ecological Classifications for Shallow Streams in Northeastern United States

Several regions in the Unites States have developed algal bioassessment methods for wadeable streams (e.g. Maine, Connecticut). Algal communities and indicator species are correlated with land use, water chemistry, and other watershed metrics to identify ecosystem indicators relevant to local conditions. Taxonomic analysis has historically been performed by microscopic examination and identification of species within a sample. A pilot survey was conducted to assess the use of DNA-based taxonomic methods in algal bioassesments of stream condition in New Hampshire and Maine in the northeastern United States. Algae samples were collected at 60 wadeable streams throughout the region in the summer of 2019. Samples were collected at sites included in long term water quality monitoring networks, to allow comparison with longer term water quality and bioassesment data. Samples were extracted and sequenced with primers targeting 18S for eukaryote species, rbcl for diatoms, and 12S for fish. Algal features were correlated with stream parameters including nutrient concentration, historic Benthic IBI indices, and other water quality metrics. Our results support previous studies indicating that molecular-based methods are a viable approach to water quality assessment. We found that: DNA-derived algal communities can be correlated to nutrient categories, and indices developed from multiyear data are reflected in the community. DNA-derived algal communities can be correlated to Benthic IBI ratios, and to traditional algal bioassesment categories. 18S and rbcl primers were both effective at amplifying target species to identify distinguishable community assemblages. Fish were detected in water samples at all sites, and the species identified represent those that are likely to be present based on previous electro-fishing surveys. DNA-derived algal communities can be correlated to nutrient categories, and indices developed from multiyear data are reflected in the community. DNA-derived algal communities can be correlated to Benthic IBI ratios, and to traditional algal bioassesment categories. 18S and rbcl primers were both effective at amplifying target species to identify distinguishable community assemblages. Fish were detected in water samples at all sites, and the species identified represent those that are likely to be present based on previous electro-fishing surveys.

Risk Indicators for Identifying Critical Source Areas in Five Arkansas Watersheds

Abstract. Change point analysis was used to explore the interactions between watershed characteristics and concentrations of nitrate-nitrogen, total nitrogen, soluble reactive phosphorus, and total phosphorus in streams within the Ozark Highlands, Arkansas Valley, and Ouachita Mountains ecoregions of Arkansas. Thresholds were identified for multiple watershed metrics used to predict water quality, including percent forest in the catchment, agricultural and forested land use in the riparian buffer, stream density, and poultry house density. Based on the observed relationships from the sampled watersheds, we propose four risk indicators to improve the identification of critical source areas for NPS pollution mitigation: subwatersheds that have less than 50% forested area within the drainage area, less than 50% forested area in the riparian buffer zone, more than 0.9 poultry houses km-2, and a stream density that exceeds 50 m ha-1. Keywords: Nonpoint-source pollution, Source water protection, Watershed management.

IDW‐Plus: An ArcGIS Toolset for Calculating Spatially Explicit Watershed Attributes for Survey Sites

AbstractWatershed characteristics such as land‐use and land‐cover affect stream condition at multiple scales, but it is widely accepted that conditions in close proximity to the stream or survey site tend to have a stronger influence. Although spatially weighted watershed metrics have existed for years, nonspatial lumped landscape metrics (i.e., areal mean or percentage) are still widely used because relatively few technical skills are needed to implement them. The Inverse Distance Weighted Percent Land Use for Streams (IDW‐Plus) custom ArcGIS toolset provides the functionality to efficiently calculate six spatially explicit watershed metrics which account for the Euclidean or flow length distance to the stream or outlet, as well as the probability for overland runoff. These include four distance‐weighted metrics, those being inverse Euclidean distance to the stream or outlet, and the inverse flow length to the stream or outlet. Two tools are also included to generate hydrologically active (i.e., runoff potential), inverse flow length to the stream or outlet metrics. We demonstrate the tools using real data from Southeast Queensland, Australia. We also provide detailed instructions, so readers can recreate the examples themselves before applying the tools to their own data.

Hydrologic response to stormwater control measures in urban watersheds

Stormwater control measures (SCMs) are designed to mitigate deleterious effects of urbanization on river networks, but our ability to predict the cumulative effect of multiple SCMs at watershed scales is limited. The most widely used metric to quantify impacts of urban development, total imperviousness (TI), does not contain information about the extent of stormwater control. We analyzed the discharge records of 16 urban watersheds in Charlotte, NC spanning a range of TI (4.1–54%) and area mitigated with SCMs (1.3–89%). We then tested multiple watershed metrics that quantify the degree of urban impact and SCM mitigation to determine which best predicted hydrologic response across sites. At the event time scale, linear models showed TI to be the best predictor of both peak unit discharge and rainfall-runoff ratios across a range of storm sizes. TI was also a strong driver of both a watershed’s capacity to buffer small (e.g., 1–10mm) rain events, and the relationship between peak discharge and precipitation once that buffering capacity is exceeded. Metrics containing information about SCMs did not appear as primary predictors of event hydrologic response, suggesting that the level of SCM mitigation in many urban watersheds is insufficient to influence hydrologic response. Over annual timescales, impervious surfaces unmitigated by SCMs and tree coverage were best correlated with streamflow flashiness and water yield, respectively. The shift in controls from the event scale to the annual scale has important implications for water resource management, suggesting that overall limitation of watershed imperviousness rather than partial mitigation by SCMs may be necessary to alleviate the hydrologic impacts of urbanization.

Technical Note: Assessing Best Management Practices Effectiveness at the Watershed Scale

Best Management Practices (BMPs) are commonly used to address water quality concerns from nonpoint source activities. BMPs must be effective to reduce impacts to acceptable levels at a watershed scale, but there is controversy about how to represent BMP effectiveness. The most common way is by calculating a percent reduction in pollutant load, but some criticize this as potentially misleading. Percent reduction is a legitimate and relatively easy to understand method of describing effectiveness, but it is only one of many ways. Other approaches include attainment of water quality or habitat standards and goals, biological response, and even economic efficiency. Perhaps the three biggest challenges for assessing BMPs directed at nonpoint source activities are defining appropriate water quality expectations (how much is enough and what is attainable), determining what site conditions limit BMP effectiveness, and determining specific watershed metrics and appropriate spatial and temporal scales for assessment. Ongoing efforts to develop beneficial and realistic numeric nutrient criteria and contemporary forest watershed studies, both using monitoring of multiple response parameters, provide examples of how weight-of-evidence approaches may be the most useful way to judge BMP effectiveness.

Effects of upstream lakes on dissolved organic matter in streams

We examined the effects of upstream lakes on dissolved organic matter (DOM) quantity and the absorbance of ultraviolet (UV) radiation in the streams of northern Michigan. We assessed DOM concentration and absorbance in 15 streams with upstream lakes and 17 streams without upstream lakes located in the same geographic region in May and August 2003. In addition, we estimated watershed land cover and morphology to assess the possibility that other landscape variables could account for DOM differences between the two stream types. The concentration of dissolved organic carbon, its UVB absorbance, and its molar absorbtivity (absorbance per unit carbon) were all significantly lower in streams with upstream lakes than in streams with no lakes. Strong predictive relationships existed between upstream watershed metrics and stream DOM properties, but varied by season and the presence of upstream lakes. DOM quantity and UV‐absorbing ability were related to different watershed metrics, with DOM quantity being strongly related to terrestrial watershed metrics, whereas UV‐absorbing ability was most strongly related to percent water surface area. Upstream lakes strongly influence downstream DOM potentially because of their long water residence times, which could increase opportunities for DOM processing. Upstream lakes represent a strong landscape predictor of stream DOM properties that is not directly tied to terrestrial DOM sources and processing.