Richard R. Horner

Nuisance biomass levels of periphytic algae in streams

Relative coverage of filamentous periphytic algae increased with chlorophyll a (chl a) biomass on natural substrata in 22 northwestern United States and Swedish streams. A biomass range of 100–150 mg chl a m−2 may represent a critical level for an aesthetic nuisance; below those levels, filamentous coverage was less than 20%. Other indices of water quality (dissolved oxygen content and measures of benthic macroinvertebrate diversity) were apparently unaffected by periphytic biomass or filamentous coverage in these streams. Neither was biomass related to limiting nutrient content (soluble reactive phosphorus, SRP), as has been observed in previous experiments using bare rocks in streams and slides in artificial channels. Ambient SRP concentration may not be a useful predicter of periphyton accrual on natural substrates, due to uptake and recycling of P throughout the stream and undetermined losses such as sloughing and grazing.

Pollutant removal from stormwater runoff by palustrine wetlands based on comprehensive budgets

Comprehensive budgets of total suspended solids (TSS), total phosphorus (TP), total zinc (the most prevalent metal in urban runoff), and fecal coliforms (FC) were developed for two palustrine freshwater wetlands in Washington, USA. These budgets were based on input (inflow, precipitation, groundwater) and output (outflow, evaporation). One wetland received runoff from a primarily urbanized watershed (187 ha), whereas the other watershed (87 ha) was mostly rural and forested. Annual loadings to the urban wetland for TSS, TP, and zinc were 107, 0.63 and 0.43 kg ha−1 yr−1, respectively, based on watershed area. Corresponding loadings to the nonurban wetland were 30, 0.62 and 0.08 kg ha−1 yr−1. High TP input from groundwater at the nonurban wetland (82% of the TP input) resulted in overall loadings comparable to the urban wetland. Fecal coliform loadings were 4.2 · 1010 and 1.4 · 109 organisms ha−1 yr−1 for the urban and nonuran wetlands, respectively. Mean annual removal percentages (over the two-year study period) for TSS, TP, zinc, and FC were estimated at 14, 8, 31, and 49%, respectively in the urban wetland (2 ha). Corresponding removal rates in the nonurban wetland (1.5 ha) were 56, 82, 23, and 29%, respectively. Pollutant removal was influenced by season, flow conditions, residence time, pollutant source (surface versus groundwater), and pollutant state (solid versus dissolved). Results for the nonurban wetland showed that groundwater inputs were significant for TP loadings and removal.

Prediction of nuisance periphytic biomass: a management approach

Abstract Model predictions of periphyton biomass, as a function of ambient SRP concentration, were compared against observed biomass accrual on natural and artificial substrates in the Spokane River, Washington. A range in biomass was predicted based on uncertainties due to temperature, velocity, accumulation period and an empirical growth constant. Only 8 of 47 observed biomass values exceed the lowest biomass predictions, which supports the contention that the model represents the maximum potential biomass. Using the SRP concentration that would produce a threshold nuisance biomass (150–200 mg ch α/m 2 ), an approach is proposed for controlling the stream distance for which periphytic biomass exceeds the nuisance level. For the Spokane River, critical distance with biomass exceeding 200 mg chl α/m 2 may exceed 10 km unless SRP is held below 10 μg/l.

Impacts of urbanization on palustrine (depressional freshwater) wetlands—research and management in the Puget Sound region

This paper summarizes the results of the Puget Sound Wetlands and Stormwater Management Research Program, which examined the impacts of urban stormwater on wetlands. Results are presented for data collected between 1988 and 1995 for 19 wetlands, showing changes in wetland hydrology resulting from urban conversion and the subsequent impacts on plant and amphibian communities. The amount of watershed imperviousness, the forested area, and the degree of outlet constriction were found to be the most significant factors affecting wetland hydroperiods. As hydroperiods changed, plant communities shifted towards communities adaptable to the new hydrograph. Wetlands with water level fluctuation above 20 cm resulted in lower plant richness in the emergent and scrub-shrub zones. Similarly, wetlands with water level fluctuation greater than 20 cm were significantly more likely to have low amphibian richness of three or fewer species. A primary goal of the research program was to employ the results to improve the management of both wetlands and stormwater in urban areas. Hydrologic guidelines were applied to King Countys basin planning and master drainage planning efforts. Controls that focused on minimizing impervious surfaces and maximizing forest retention in the wetland watershed proved to be the most widely usable strategy.

Stream periphyton response to grazing and changes in phosphorus concentration

Grazing by the large caddisfly larva, Dicosmoecus gilvipes (Trichoptera; Limnephilidae), drastically reduced periphyton biomass in laboratory channels at a current velocity of 20 cm s−1. Reduction in biomass as chl a and AFDW ranged from 88 to 93% and 82 to 85%, respectively. On average, grazing rate increased with in-channel SRP (soluble reactive phosphorus) content from 6 to 10 µg 1−1. Grazing rates averaged 25.9–29.3 µg chl a m−2 d−1 and 10.8–12.2 µg chl a mg−1 d−1 based on area and grazer biomass, respectively, with most variability among treatments being due to the grazing effect. Grazing tended to shift the algal community increasingly to filamentous blue-green algae regardless of enrichment. After three weeks, Phormidium comprised over 61% of the community in grazed treatments but only 35% in ungrazed treatments. The stalked diatom Gomphonema comprised only 4% of the grazed community, but 11% in the three ungrazed channels with similar values for Scenedesmus. A model that includes grazing was calibrated to the data and produced a reasonable expectation of periphyton biomass over a range in SRP concentrations. While the model with constant grazer abundance predicts a gradually increasing grazed biomass as SRP increases, grazer production in natural streams may actually increase to accommodate the increased food production.

STRUCTURAL AND NON-STRUCTURAL BMPS FOR PROTECTING STREAMS

Stream ecosystems in three different locations in the United States were found to benefit in a similar fashion from retention of watershed forest and wetland cover and wide, continuous riparian buffers with mature, native vegetation. The findings can help guide comprehensive watershed management and application of these non- structural practices in low-impact urban design. Intensive study of structural best management practices (BMPs) in one location found that, even with a relatively high level of attention, a minority of the developed area is served by these BMPs. Those BMPs installed are capable of mitigating an even smaller share of urban impacts, primarily because of inadequacies in design standards. Even with these shortcomings, though, results showed that structural BMPs help to sustain aquatic biological communities, especially at moderately high urbanization levels, where space limits non-structural options.

Environmental evaluation of calcium magnesium acetate for highway deicing applications

Abstract Calcium magnesium acetate (CMA) was identified in the early 1980s as a material that is potentially effective for deicing highways, feasible to manufacture commercially, and environmentally acceptable. Its environmental acceptability required definitive testing prior to widespread application. This paper reports the results of comprehensive laboratory and controlled field plot experiments designed to determine CMA transport characteristics and environmental fate and its impacts on terrestrial and aquatic ecosystems. Preliminary modeling predicted routine and maximum CMA concentrations and mass loadings in highway runoff and spray as a basis for designing experimental treatments. In experiments testing CMA effects on a number of soil physical properties, only permeability exhibited any substantial change; however, the general increases in this characteristic are not a cause for concern relative to CMA use. Laboratory assessments of soils dosed with CMA solutions showed potential acetate mobility, yet field measurements yielded only minor evidence of CMA transport in the soil and ground water. The laboratory experiments also demonstrated a potential to release certain trace metals, preexisting in soils, through ion exchange reactions involving calcium and magnesium, a trend confirmed in the field, although with less strength and consistency. The quantities released in these experiments would pose no environmental hazards, but it is unknown whether mobilization from heavy metal-contaminated actual roadside soils would do so. CMA biodegradation was investigated at several temperatures in both soils and water. At 20 and 10°C, a high level of decomposition was achieved within 2 weeks in soils, and most of the ultimate BOD was exerted within 5 and 10 days, respectively, in water. These levels of decomposition required 4 weeks in soils and 100 days in water at 2°C. Biodegradation in water was associated with the leading potential environmental impact of concern, the ability of CMA in concentrations that could be found in highway runoff to deplete dissolved oxygen in water; this issue is the subject of a companion paper. In greenhouse pot tests of CMA effects on various herbaceous and woody plant species, only root zone concentrations well above any normally expected value killed seedlings. Field applications of similarly high concentrations did not affect the yield, cover, vigor, rooting, or leaf condition of the plot flora. A series of laboratory bioassays on zooplankton and fish resulted in high rates of survival and reproduction at any routinely expected CMA concentration, so long as oxygen was not allowed to deplete.

Non-point source water pollution management: Improving decision-making information through water quality monitoring*

The identification, assessment and management of non-point source water pollution problems can be improved through better water quality monitoring program designs. The result is often more useful and reliable information for use by decision-makers. In this study of the Svart River Basin in south-central Sweden, the results of a modified monitoring program, designed to address non-point source inputs, were compared with the results of the ongoing program. Cost, validity (addressing intended objectives) and reliability (estimated level of uncertainty) were the criteria used to evaluate and compare the design and results obtained from the two programs. The study showed that choices of variables measured, station location and sampling frequency have a direct influence on the type and value of information obtained, especially when considering non-point sources. For a similar cost, the modified program produced more valid and reliable information for decision-making than the ongoing program.

Effects of calcium magnesium acetate (CMA) on dissolved oxygen in natural waters

Abstract Comprehensive laboratory and field experiments were performed to determine the potential effects of the experimental deicing agent calcium magnesium acetate (CMA) on aquatic and terrestrial ecosystems. A companion paper covers the overall results of these experiments. This paper concentrates on the leading concern to emerge from the testing, the potential for CMA to deplete dissolved oxygen (DO) in water bodies. In laboratory biochemical oxygen demand (BOD) experiments, 100 mg CMA/1, at the high end of the concentration routinely expected in highway runoff, completely depleted oxygen within 2 days at 20°C. A concentration of 10 mg/1 caused a net depletion of about 4.5 and 7.0 mg O2/l for reagent-grade and corn-based CMA, respectively. This extra oxygen demand was created by the corn-based CMA even though the two products had equal acetate concentrations. Most of the extra demand can probably be attributed to the presence of butyrate as a contaminant in the corn-based CMA. The rate of DO depletion was strongly dependent on temperature. While the rate appeared to follow an Arrhenius relationship with temperature, the classic, first-order BOD equation did not represent initial DO depletion well at low temperatures. An alternative model was proposed for this region, where depletion better followed a logistic-type curve, probably in direct proportion to the growth of bacteria. Oxygen depletion after CMA additions was also observed in microcosm ecosystems and field ponds, although reaeration reduced net depletion compared to the BOD experiments. When ice covered one of the ponds, a large DO drop occurred following a relatively small CMA inflow. It is recommended that CMA applications be avoided in situations where receiving waters are close to the road, have a low dilution potential, or support populations of fish sensitive to low oxygen levels. Applications during late spring storms and where there is potential for CMA runoff to get into ice-covered water bodies are also discouraged.

RESPONSE OF LAKE SAMMAMISH TO URBAN RUNOFF CONTROL

ABSTRACT A seasonal phosphorus model was used to predict the effect of proposed watershed development on water quality in Lake Sammamish, Wash. The model was calibrated and verified using daily loadings from two separate annual data sets. Phosphorus yields were scaled from literature values using actual loadings. Results indicate that substantial runoff controls should be applied to maintain water quality at its present, near oligotrophic state and prevent its return to a prewastewater diversion mesotrophic–eutrophic state.