Eugene B. Welch

Suggested classification of stream trophic state: distributions of temperate stream types by chlorophyll, total nitrogen, and phosphorus

Abstract Aquatic scientists and managers have no conventional mechanism with which to characterize and compare nutrients and algal biomass in streams within a broader context analogous to trophic state categorization in lakes by chlorophyll (chl) and nutrients. We analyzed published data for a large number of distinct, temperate, stream sites for mean benthic chl ( n =286), maximum benthic chl ( n =176), sestonic chl ( n =292), total nitrogen ( n =1070), and total phosphorus ( n =1366) as a first effort to establish criteria for trophic boundaries. Two classification systems are proposed. In the first system, the boundary between oligotrophic and mesotrophic categories is defined by the lower third of the cumulative distribution of the values. The mesotrophic–eutrophic boundary is defined by the upper third of the distribution. In the second system, individual streams are placed more precisely in a broad geographic context by assessing the proportion of streams that have greater or lesser nutrient and chl values. The proposed relationships for streams were compared to trophic criteria published for lakes. The proposed trophic boundaries for streams generally include a broader range of values in the mesotrophic range than conventional criteria for lakes. The ratio of maximum to mean benthic chl for streams was significantly higher than that found for planktonic chl in lakes, reflecting the greater variance in streams. This high variance in streams suggests that the proposed stream trophic criteria should be viewed only as a general first approach to categorizing stream ecosystems.

Effectiveness and Longevity of Phosphorus Inactivation with Alum

ABSTRACT Effectiveness and longevity of alum treatments were evaluated in 21 lakes (or lake basins) across the United States; 9 were polymictic and 12 were dimictic. Effectiveness was judged from reductions in lake TP (total phosphorus) and internal loading rate, as well as chlorophyll a (chl a), both initially and over periods ranging from 4 to 20 years following treatment. Internal loading rate was reduced in six of nine polymictic lakes/basins by an average of two-thirds, and lake TP was reduced by about one-half, which persisted for 5–11 years. Internal loading rate in dimictic lakes (7 of 7 with adequate data) remained reduced by an average of 80% for 4 to 21 years (average 13 yrs). For the six polymictic lakes, in which treatment was effective, chl a decreased by an average of two-thirds initially, but was about 40% less than die pre-treatment level after 5 to 11 years. Chl a decreased in seven dimictic lakes by an average of 57% initially and 42% after 5–18 years. In some cases, response was indepe...

Internal Phosphorus Loading in Shallow Lakes: Importance and Control

Abstract Decreasing the algal biomass and increasing transparency in shallow, unstratified lakes is usually more difficult than for deep, stratified lakes. Eutrophic unstratified lakes (or shallow, stratified lakes susceptible to metalimnion erosion) have typically responded slowly to reduced external nutrient loading, usually because of longevity of internal loading. That is because sediment-released nutrients (especially phosphorus) readily enter the trophogenic zone of shallow lakes during the growing season and result in high lake concentrations. In stratified lakes, metalimnia may serve as barriers to phosphorus transport into the trophogenic zone. Although the whole water column in shallow lakes is usually aerobic, several mechanisms can combine to produce relatively high sediment phosphorus release rates in these lakes. These include: 1) wind resuspension and bioturbation, combined with high pH or low Fe/P ratio that maintains high P solubility, 2) periodic anoxia and reducing conditions promoted by calm, warm weather, and 3) macro-phyte senescence. Attempts to reduce algal biomass by controlling internal phosphorus loading have often been effective.

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.

Effectiveness of Al, Ca, and Fe salts for control of internal phosphorus loading in shallow and deep lakes

Internal P loading can maintain high P concentrations and delay eutrophic lake recovery following abatement of external loading. Sediment P inactivation with Al salts has been shown to provide long-term (5–14 years) control of sediment P release; long-term effectiveness of Fe and Ca salts has not been reported. Al toxicity problems are possible unless pH is maintained in the 6–8 range. Vertical transport of hypolimnetic P is unlikely in small, deep, dimictic lakes (\-Z√A0 > 8), and effectiveness of P inactivation in lowering their mid-summer epilimnetic P has not been demonstrated. To date, P inactivation has been found to be most effective in improving trophic state in shallow, softwater, polymictic lakes where control of sediment P release affects the entire water column. Abatement of external loading, where necessary, is essential for a successful P inactivation treatment.

Internal phosphorus loading in a shallow eutrophic lake

Abstract Internal loading of phosphorus has been implicated as a major eutrophicating factor in Long Lake, Washington (Kitsap County). As a result of such loading, summer total phosphorus concentrations approach or exceed 100 μgP l −1 . Most of the summer loading of phosphorus is thought to have been released directly from the rich, flocculent sediment in the mid and northern part of the lake as a result of high pH (up to 10) related to phytoplankton photosynthesis. The lake also supports a dense submersed macrophyte crop (areal weighted mean dry weight of about 220 g m −2 ) composed primarily of Elodea densa . Although excretion of phosphorus from healthy E. densa was found to be minimal, the potential contribution of P indirectly from sediment via macrophyte uptake and subsequent decomposition in the winter was on the order of 200–400 kg yr −1 or about 25–50% of the external loading. Nevertheless, loading of phosphorus during predrawdown summers is thought to have originated largely as a direct release from sediment due to high pH. Estimates of sediment phosphorus release determined from laboratory experiments, mass balance and core analyses ranged from 2.2 to 5.6 mg m −2 day −1 . As a component of the restoration program, the lake (mean depth of 2 m) was drawn down nearly 2 m for 4 months during the summer and fall of 1979. The lakes trophic status was expected to improve due to sediment consolidation and/or macrophyte reduction. The drawdown resulted in an 84% reduction in macrophyte biomass in 1980 but minimal sediment consolidation (0.1 m). Winter decomposition of the much smaller macrophyte crop, apparently provided insufficient phosphorus in the spring to stimulate phytoplankton and to enrich midlake sediments, which has probably occurred in previous years. Low water column pH during the postdrawndown summer of 1980 resulted from relatively low rates of plankton photosynthesis. During the summer of 1980 internal loading of phosphorus was reduced and total phosphorus remained below 50 μg l −1 .

Dosing Alum to Wisconsin Lake Sediments Based on in vitro Formation of Aluminum Bound Phosphate

ABSTRACT The dose of aluminum (Al) needed to deplete mobile inorganic sediment phosphorus (P) [loosely-sorbed P and Iron (Fe)-bound P] and transform it to Al-P was estimated in vitro in Lake Delavan, Wind Lake, and Bass Bay sediments. The formation of Al-P was logarithmically related to increased Al added as buffered alum. Results of the in vitro treatments were compared with the observed effect on sediment-P composition from the 1991 alum treatment (12 g Al·m−2) in Lake Delavan. That 1991 dose resulted in the formation of 2.2 g P·m−2, measured as Al-P, which was apparently the maximum amount of P that could be adsorbed with that alum dose. Based on in vitro alum additions, 150 g Al·m−2, twelve times that added, would have been required to nearly deplete mobile P in surface (0–4 cm) sediment of Lake Delavan (16 m). Wind Lake contained less mobile P, so a dose of 80 g Al·m−2 was required to remove mobile P in sediments from its deep hole (14m), while an addition of only 20 g Al·m−2 was needed for sediments...

Periphyton biomass related to point-source nutrient enrichment in seven New Zealand streams

Periphyton biomass on natural substrata at 26 sites above and below point source discharges in 7 New Zealand streams was compared with maximum potential values predicted by a laboratory calibrated model to determine the extent to which biomass was controlled by nutrients. Point-source enrichment, which increased dissolved reactive phosphorus (DRP) from 6 to 100 times the saturation level (about 25 μg/l) in five streams, was found to substantially increase biomass at all enriched sites in four streams. In two of these streams, biomass below the enrichment inputs was about 1200 mg chl a/m2. Overall, biomass averaged only 35 ± 44% of that predicted from phosphorus, velocity and temperature using the model. Furthermore, aesthetically nuisance biomass levels (i.e. > 200 mg chl a/m2) were observed at only 7 of the 19 downstream sites. In many cases, the lower than expected biomass levels were associated with high macroinvertebrate grazer densities, riparian shading or unsuitable attachment surfaces. These factors, therefore, appear to have exercised more control on periphyton biomass than nutrients, and may offer more effective alternatives for biomass control in enriched streams than lowering DRP below biomass saturating levels.

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.

Lake trophic state change and constant algal composition following dilution and diversion

Abstract As a result of adding low-nutrient dilution water and diverting sewage effluent, the trophic state of 2790 ha Moses Lake in eastern Washington, USA, changed from hypereutrophic to slightly eutrophic. Total phosphorus and chlorophyll a decreased by over 70% and apparently reached an equilibrium in 1986–1988, following the start of dilution in 1977 and diversion of sewage effluent in 1984. Transparency increase was greater than expected from chlorophyll a reduction, due to dilution of non-algal matter. However, the lake segment that received sewage is shallow and turbid due to entrainment of particulate matter by wind and carp, and therefore showed only a slight increase in transparency. In spite of the substantial trophic-state change, algal species composition remained about the same as before treatment; blue-green algae averaged more than 60% for the spring-summer period. Green algae also unexpectedly remained dominant in the lake segment that received sewage even though there was a large decrease in biomass. Persistence by green algae may be due to removal of blue greens by attachment to clay particles and sinking, thereby interfering with their buoyancy control mechanism. On the other hand, continued blue-green dominance in other segments of the lake may be due to low average free CO 2 content and N/P ratios remaining at N-limiting levels. Large sediment-to-water inoculations of blue greens probably continue as well.