The effect of piping stream channels on dissolved oxygen concentration and ecological health.

Sunlight plays a key role in the nutrient cycle within streams. Streams are often piped to accommodate urban residential or commercial development for buildings, roads, and parking. This results in altered exposure to sunlight, air, and soil, subsequently affecting the growth of aquatic vegetation, reducing reaeration, and thus impairing the water quality and ecological health of streams. While the effects of urbanization on urban streams, including changing flow regimes, stream bank and bed erosion, and degraded water quality, are well understood, the effects of piping streams on dissolved oxygen (DO) concentrations, fish habitats, reaeration, photosynthesis, and respiration rates are not. We addressed this research gap by assessing the effects of stream piping on DO concentrations before and after a 565-m piped section of Stroubles Creek in Blacksburg, VA, for several days during the summer of 2021. Results indicate that the DO level decreased by approximately 18.5% during daylight hours as water flowed through the piped section of the creek. Given the optimum DO level (9.0 mg·L-1) for brook trout (Salvelinus sp.), which are native and present in a portion of Stroubles Creek, the resulting DO deficits were - 0.49 and - 1.24 mg·L-1, for the inlet and outlet, respectively, indicating a possible adverse impact from piping the stream on trout habitat. Photosynthesis and respiration rates were reduced through the piped section, primarily due to the reduced solar radiation and the resultant reduction in oxygen production from aquatic vegetation; however, the reaeration rate increased. This study can inform watershed restoration efforts, particularly decisions regarding stream daylighting with respect to potential water quality and aquatic habitat benefits.

Using Random Forest, a machine learning approach to predict nitrogen, phosphorus, and sediment event mean concentrations in urban runoff.

Estimating pollutant loads from developed watersheds is vitally important to reduce nonpoint source pollution from urban areas, as a key tool in meeting water quality goals is the implementation of Stormwater Control Measures (SCMs). SCMs are selected and sized based on influent pollutant loads. A common method used to estimate pollutant loads in urban runoff is the Event Mean Concentration (EMC) method. In this study, we develop and apply data-driven models using Random Forest (RF), a machine learning approach, to predict Total Nitrogen (TN), Total Phosphorus (TP), Total Suspended Solids (TSS), and Ortho-Phosphorus (Ortho-P) EMCs in urban runoff. The parameters considered in this study were climatological characteristics (i.e., Antecedent Dry Period or ADP, Precipitation Depth or P, Duration or D, and Intensity or I) and catchment characteristics including land use-related parameters including Imperviousness or Imp, Saturated Hydraulic Conductivity or Ksat, and Available Water Capacity or AWC), and site-specific parameters including Slope (S), and Catchment Size (A). Stormwater quality data for this study were obtained from the National Stormwater Quality Database (NSQD), which is the largest repository of stormwater quality data in the U.S. Results demonstrate that land use-related characteristics (i.e., Imp, Ksat, and AWC) were the most effective variables for predicting all EMCs. For TP, TSS, and Ortho-P, site-specific characteristics (S and A) had a greater effect than climatological characteristics (i.e., ADP, P, D, and I). However, for TN, climatological characteristics had a greater effect than site-specific characteristics (S and A). In addition, for TN, TP, and TSS, precipitation characteristics (P, D, and I) were found to be more effective parameters for estimating EMCs than ADP. This study highlights the most influential parameters affecting EMCs which can be used by stakeholders and SCMs designers to improve estimates of nutrients and sediment EMCs. The selection and design of the highest performing SCMs is essential in achieving effective treatment of stormwater, attaining water quality goals, and protecting downstream waterbodies.

Effect of intermittent aeration mode on nitrogen concentration in the water column and sediment pore water of aquaculture ponds.

Nitrogen in pond sediments is a major water quality concern and can impact the productivity of aquaculture. Dissolved oxygen is an important factor for improving water quality and boosting fish growth in aquaculture ponds, and plays an important role in the conversion of ammonium-nitrogen (NH4+-N) to nitrite-nitrogen (NO2--N) and eventually nitrate-nitrogen (NO3--N). A central goal of the study was to identify the best aeration method and strategy for improving water quality in aquaculture ponds. We conducted an experiment with six tanks, each with a different aeration mode to simulate the behavior of aquaculture ponds. The results show that a 36 hr aeration interval (Tc = 36 hr: 36 hr) and no aeration resulted in high concentrations of NH4+-N in the water column. Using a 12 hr interval time (Tc = 12 hr: 12 hr) resulted in higher NO2--N and NO3--N concentrations than any other aeration mode. Results from an 8 hr interval time (Tc = 8 hr: 8 hr) and 24 hr interval time (Tc = 24 hr: 24 hr) were comparable with those of continuous aeration, and had the benefit of being in use for only half of the time, consequently reducing energy consumption.

What are the relevant sources and factors affecting event mean concentrations (EMCs) of nutrients and sediment in stormwater?

Urbanization increases runoff, sediment, and nutrient loadings downstream, causing flooding, eutrophication, and harmful algal blooms. Stormwater control measures (SCMs) are used to address these concerns and are designed based on inflow loads. Thus, estimating nutrient and sediment loads is important for meeting restoration objectives. Pollutants accumulate on surfaces during dry periods, making Event Mean Concentration (EMC) a function of antecedent dry period (ADP). An EMC results from wash-off of accumulated pollutants from catchment surface during runoff events. However, several studies found little to no correlation between constituent concentrations in stormwater and ADP. The objective of this study is to verify this finding and discover which climatological or catchment characteristics most significantly affect stormwater quality. Stormwater quality data were obtained from the National Stormwater Quality Database (NSQD), which is the largest data repository of stormwater quality data in the U.S. Bayesian Network Structure Learner (BNSL) was used to assess the relationships between catchment characteristics, climatological information, and stormwater quality for selected land uses. Given the optimal BN structure, it was determined which parameters most affect stormwater quality EMCs. The results demonstrate that both catchment and rain characteristics affected stormwater quality EMCs. Among catchment characteristics, land use (LU) was the most important factor and catchment size was the least. Precipitation depth (P) and duration (D) affected Total Phosphorus (TP), Total Nitrogen (TN), and Total Suspended Solids (TSS). This indicated that it is likely that P and D had a greater influence on stormwater quality more than ADP. P, D, and ADP affected the dissolved constituents of TN (i.e. NO2-N/NO3-N) and TP (i.e. Ortho-P). Compared to other factors (i.e. P and D), the effect of ADP on TSS was negligible. Stormwater quality EMCs related to nitrogen were not affected by catchment slope (S). However, TSS and Ortho-P were influenced by S.

The effect of temperature on sulfate release from Pearl River sediments in South China.

Sulfate (SO42-) has received attention as means of monitoring water quality and pollution. However, the SO42- content of rivers, lakes, and reservoirs varies significantly by season, so environmental factors such as temperature can affect it. An experiment was conducted with a series of aerobic and anaerobic tanks containing Pearl River sediments and distilled water to assess the release of SO42- from sediments under controlled conditions. "Black-odor river" refers to near anoxic conditions in the water column and foul odors emanating from affected rivers in southeastern China. These river systems typical have sediments containing ammonia (NH3), hydrogen sulfide (H2S), and organic sulfide compounds in excess, and precipitates of sulfide (S2-), with ferrous (Fe2+) or manganese (Mn2+). SO42- concentration was measured at various depths in pore water and in the water column while controlling temperature and dissolved oxygen (DO) concentrations. Interpolation of study results revealed that SO42- content was highest between temperatures of 20 °C and 25 °C. The relationship between SO42- concentration, which varied with temperature and time, was fit using a linearized Michaelis-Menten function (R2 = 0.69). The release of SO42- to the water column was accelerated during the experiment (for temperatures higher than 20 °C), and led to higher SO42- content in the water column than in pore water. The maximum concentration of SO42- within the sediment occurred at a temperature of 20 °C. Comparing aerated and non-aerated tanks at 20 °C, we found that O2 restricted SO42- content in the water column; DO could, in turn, also be controlled by temperature. Fe2+ and Mn2+ had a negative correlation with SO42-.

Simulation of watershed-scale practices for mitigating stream thermal pollution due to urbanization.

Thermally enriched runoff from urban impervious surfaces can be harmful to aquatic life; however, only limited information is available on how to mitigate these impacts at the watershed-scale. This study evaluates the effects of retrofitting an urban watershed with thermal mitigation practices (TMPs) relative to thermal toxicity thresholds for aquatic species. The Minnesota Urban Heat Export Tool (MINUHET) and Storm Water Management Model (SWMM) models were used to evaluate TMPs that help reduce temperature and total heat loads (THL) from the Stroubles Creek watershed in Blacksburg, Virginia. We used the aquatic health criteria for brook trout (Salvelinus fontinalis), the most sensitive species present downstream of the watershed, as a performance measure. TMPs included bioretention systems, methods for reducing the albedo of surfaces (cool surfaces), and increasing forest canopy. Performance metrics included Event Mean Temperature (EMT), and the Percentage of Time Temperature Exceeded the 21 °C Acute Toxicity Threshold [Percentage of Time above the Threshold (PTAT)] for brook trout; these metrics were used to quantify reductions in heat loads and temperatures. TMPs were evaluated during continuous simulation and selected storm events. Increased forest canopy alone produced the greatest reduction of stream temperature, as quantified by EMT and PTAT metrics during continuous and event-based simulations. In contrast, cool surfaces reduced THL more than any other individual TMP for the continuous simulation. A comprehensive mitigation plan (CMP) integrating all three TMPs reduced THL by 62.3%, and PTAT by approximately 12%, for the entire summer of 2015. The CMP was also applied to select storm events, during which streamflow EMT was reduced up to 9%, and PTAT was reduced nearly to zero. This study, which is the first to simulate watershed-scale TMPs for a large, complex urban area, demonstrates the application of appropriate strategies for restoring aquatic habitats in the thermally impacted Stroubles Creek.

Water quality characterization of storm and irrigation runoff from a container nursery.

Commercial nurseries grow specialty crops for resale using a variety of methods, including containerized production, utilizing soilless substrates, on a semipervious production surface. These "container" nurseries require daily water application and continuous availability of mineral nutrients. These factors can generate significant nutrients [total nitrogen (TN), and total phosphorus (TP)] and sediment [total suspended solids (TSS)] in runoff, potentially contributing to eutrophication of downstream water bodies. Runoff is collected in large ponds known as tailwater recovery basins for treatment and reuse or discharge to receiving streams. We characterized TSS, TN, and TP, electrical conductivity (EC), and pH in runoff from a 5.2 ha production portion of a 200-ha commercial container nursery during storm and irrigation events. Results showed a direct correlation between TN and TP, runoff and TSS, TN and EC, and between flow and pH. The Storm Water Management Model (SWMM) was used to characterize runoff quantity and quality of the site. We found during irrigation events that simulated event mean concentrations (EMCs) of TSS, TN, and TP were 30, 3.1 and 0.35 mg·L-1, respectively. During storm events, TSS, TN and TP EMCs were 880, 3.7, and 0.46 mg·L-1, respectively. EMCs of TN and TP were similar to that of urban runoff; however, the TSS EMC from nursery runoff was 2-4 times greater. The average loading of TSS, TN and TP during storm events was approximately 900, 35 and 50 times higher than those of irrigation events, respectively. Based on a 10-year SWMM simulation (2008-2018) of runoff from the same nursery, annual TSS, TN and TP load per ha during storm events ranged from 9230 to 13,300, 65.8 to 94.0 and 9.00 to 12.9 kg·ha-1·yr-1, respectively. SWMM was able to characterize runoff quality and quantity reasonably well. Thus, it is suitable for characterizing runoff loadings from container nurseries.