Effects of Regional Climate and BMP Type on Stormwater Nutrient Concentrations in BMPs: A Meta-Analysis.

Nutrient treatment performance of stormwater best management practices (BMPs) is highly variable. Improved nutrient management with BMPs requires a better understanding of factors that influence stormwater BMP treatment processes. We conducted a meta-analysis of vegetated BMPs in the International Stormwater BMP Database and compared influent and effluent nitrogen and phosphorus concentrations to quantify the BMP effect on nutrient management across climates. BMP effect on nutrient concentration change was compared between vegetated BMPs in wet and dry climates. We examined paired dissolved inorganic nitrogen (DIN), total nitrogen (TN), dissolved inorganic phosphorus (DIP), total phosphorus (TP), and combinations of these analytes as dissolved inorganic ratios and N:P ratios. Meta-analysis with subgroup analysis was used to determine differences between wet and dry climates and among vegetated BMP types. We found that across both wet and dry climates, BMPs leach DIP and TP, increase the fraction of dissolved inorganic P (DIP:TP), and decrease dissolved N:P ratios. Dry-climate BMPs leach DIP and TP more consistently and at a higher magnitude than wet-climate BMPs, and bioretention leaches more DIP than grass strips and swales. These findings generally align with biogeochemical cycling, differences in influent chemistry, and BMP design types and goals.

Establishing three warm-season turfgrasses with tailored water: I. Growth, cover, and nitrate leaching losses.

Although treated effluent is being increasingly used to irrigate mature turfgrass, information on its use to establish grass is limited. Greenhouse experiments were conducted in 2015 and 2017 to examine establishment and nitrate leaching from three warm-season grasses: buffalograss [Buchloe dactyloides (Natt.) Eng.] 'SWI 2000', inland saltgrass [Distichlis spicata (L.) Greene], and bermudagrass [Cynodon dactylon (L.) Pers.] 'Princess77'. All grasses were grown with tailored (tertiary treated effluent with 15 mg L-1 of NO3 -N) water. Grasses were established from seed in a loamy sand and irrigated with either tailored or potable water plus granular Ca(NO3 )2 fertilizer. Leachate collected at 10- and 30-cm depths was analyzed for NO3 -N and electrical conductivity. Overall, establishment was faster and coverage was greater in 2015 than in 2017, but neither differed between irrigation treatments when grasses were analyzed separately. At the end of both establishment periods, bermudagrass and buffalograss coverage was generally greater than that of inland saltgrass. In 2017, bermudagrass irrigated with tailored water resulted in greater coverage than buffalograss or inland saltgrass. In 2015, nitrate concentrations were greater in leachate collected from bermudagrass and inland saltgrass irrigated with tailored water than from grasses irrigated with potable water. Nitrate concentrations in leachate were generally lower in 2017, reaching a maximum value of 65.3 mg L-1 when averaged over all treatment combinations, and did not differ between treatments. Our data suggest that the three grasses studied can be successfully established from seed using tailored waters.

Establishing three warm-season turfgrasses with tailored water: II. Root development, nitrate accumulation in plant tissue and soil, and relationship with leaching.

Greenhouse experiments were conducted in 2015 and 2017 to assess the feasibility of establishing three warm-season grasses-buffalograss [Buchloe dactyloides (Natt.) Eng.] 'SWI 2000', inland saltgrass (Distichlis spicata L.), and bermudagrass (Cynodon dactylon L.) 'Princess77'-with tailored water (tertiary treated effluent with 15 mg L-1 of NO3 -N) and to examine the impact on nitrate accumulation in soils and plant tissue and on root development. Grasses were established from seed in a loamy sand and irrigated with either tailored or potable water plus granular Ca(NO3 )2 fertilizer. Leachate collected at 10- and 30-cm depths was analyzed for NO3 -N and electrical conductivity. Root samples were collected to measure root length density (RLD) and root surface area (RSA). Weekly clippings were collected to determine total clipping yield and measure N content. Generally, there was no difference in establishment, RLD, or RSA between the two irrigation treatments. Highest RLD values were reported for bermudagrass, followed by buffalograss and inland saltgrass. Correlation analyses suggest that nitrate levels in leachate were lower in faster-growing grasses and in grasses with more extensive root systems, compared with slower-growing grasses with less roots, regardless of fertilization treatment. Total N in clippings was highest in inland saltgrass and lower in buffalograss and bermudagrass, indicating that N was limiting for faster-growing grasses. More research is needed to determine optimal N rates for establishing grasses that both optimize growth and minimize nitrate leaching.

A surface renewal model for unsteady-state mass transfer using the generalized Danckwerts age distribution function.

The recently derived steady-state generalized Danckwerts age distribution is extended to unsteady-state conditions. For three different wind speeds used by researchers on air-water heat exchange on the Heidelberg Aeolotron, calculations reveal that the distribution has a sharp peak during the initial moments, but flattens out and acquires a bell-shaped character with process time, with the time taken to attain a steady-state profile being a strong and inverse function of wind speed. With increasing wind speed, the age distribution narrows significantly, its skewness decreases and its peak becomes larger. The mean eddy renewal time increases linearly with process time initially but approaches a final steady-state value asymptotically, which decreases dramatically with increased wind speed. Using the distribution to analyse the transient absorption of a gas into a large body of liquid, assuming negligible gas-side mass-transfer resistance, estimates are made of the gas-absorption and dissolved-gas transfer coefficients for oxygen absorption in water at 25°C for the three different wind speeds. Under unsteady-state conditions, these two coefficients show an inverse behaviour, indicating a heightened accumulation of dissolved gas in the surface elements, especially during the initial moments of absorption. However, the two mass-transfer coefficients start merging together as the steady state is approached. Theoretical predictions of the steady-state mass-transfer coefficient or transfer velocity are in fair agreement (average absolute error of prediction = 18.1%) with some experimental measurements of the same for the nitrous oxide-water system at 20°C that were made in the Heidelberg Aeolotron.