ALBERT

Notes: 1. Phosphorus (P) release from bottom sediments is an important source of nutrient enrichment in many lakes in sedimentary basins, such as those in western Canada. On the Boreal Plain, sediment P release is particularly strong during periods of seasonal anoxia.2. In this study, the effects of reduction–oxidation (redox)-sensitive and -insensitive chemicals on P release were examined in sediment cores collected from three eutrophic lakes.3. Contrary to expectations, redox-sensitive treatments were no more effective at lowering total phosphorus (TP) in sediment cores than some redox-insensitive treatments. Redox-sensitive treatments with FeCl3 and FeCl3 + O2 reduced TP to 8 and 6%, respectively, of reference concentrations, whereas redox-insensitive treatments with alum or lime + alum reduced TP to 14% of reference concentrations. Lime and O2 treatments reduced TP concentrations to 35 and 52% of reference concentrations, respectively.4. The fraction of P that adsorbed and co-precipitated with iron and aluminium in the sediment cores was low (non-apatite phosphorus fractions 〈 5%), suggesting that P release was controlled by apatite solubility and bacterial metabolism.

Notes: 1. The main focus of this study was to investigate the effects of single and multiple moderate doses of lime (slaked lime, Ca(OH)2, and/or calcite, CaCO3) on eutrophic hardwater lakes. This information would contribute to strategies to manage phytoplankton and macrophyte biomass in eutrophic lakes.2. Water chemistry and biota were monitored for up to 7 years after initial lime treatment and results were compared with reference systems.3. Complementary studies investigated the effect of lime on macrophytes in ponds, irrigation canals and microcosm experiments.4. When water pH was kept within its natural range (≤ 10), single and multiple lime applications to lakes and ponds controlled macrophyte biomass, without negatively affecting invertebrate communities.5. Single lime treatments at moderate dosages of lakes and ponds resulted in variable and mostly temporary changes in chlorophyll a (chl a) and phosphorus (P) concentration. Although sediment P release was reduced in single-dose lakes during the first winter following treatment, reductions appeared temporary.6. Multiple treatments of lakes and ponds were effective at reducing both chl a and P concentrations over longer periods. Mean winter P release rate was also reduced after initial treatment.7. In laboratory studies, sediment cores were incubated with eight different treatments to assess P release. Redox-sensitive treatments were no more effective at lowering total P concentration in overlying water than some redox-insensitive treatments. Lime reduced total P concentrations, but was not as effective as treatments with alum.8. The use of lime in managing macrophyte and phytoplankton biomass in shallow, hardwater lakes and ponds may be preferable over other treatments, because lime is economical and non-toxic as long as pH is kept within a natural range.

Notes: 1. Two hardwater eutrophic lakes of central Alberta were subjected to single doses of Ca(OH)2 (74 or 107 mg L–1). The effects of lime treatment on phosphorus (P) precipitation, sediment P release, and macrophyte biomass were assessed for up to 2 years.2. In both lakes, sediment P release was reduced to 16 and 27%, respectively, of pre-treatment values by the first winter following treatment. However, sediment P release returned to pre-treatment values during the following year.3. In contrast to these short-term effects, macrophyte biomass decreased by as much as 80% after lime application and remained there for at least 2 years.4. Our results indicate that a single dose of Ca(OH)2 may give short-term (〈 1 year) control of P and long-term control (〉 1 year) of macrophytes in hardwater eutrophic lakes of Alberta.

Notes: 1. The impact of whole-lake lime (slaked lime, Ca(OH)2, and/or calcite, CaCO3) addition on plankton communities was evaluated in eutrophic hardwater lakes on the North American Boreal Plain.2. Two lakes received a single treatment of lime (Ca(OH)2 at 74 or 107 mg L–1), two lakes received multiple treatments with Ca(OH)2 and/or CaCO3 (5–78 mg L–1), and four lakes were untreated and served as reference systems.3. Over the long-term (〉 1 year), phytoplankton biomass was reduced in multiple-dose lakes, but not in single-dose lakes. Cyanobacteria typically dominated the algal community in the years before, during and after lime treatment in both single- and multiple-dose lakes.4. In the single-dose lakes, randomized intervention analysis showed no significant change in the biomass of zooplankton after lime addition.

Notes: 1. Whole-lake experiments were conducted in two hardwater lakes (Halfmoon and Figure Eight) in Alberta, Canada, to investigate the effectiveness of repeated lime (slaked lime: Ca(OH)2 and/or calcite: CaCO3) treatments (5–78 mg L–1) for up to 7 years.2. Randomized intervention analysis of intersystem differences between the experimental and three reference lakes demonstrated a decline in euphotic total phosphorus and chlorophyll a concentrations in the experimental lakes after repeated lime treatments.3. After the second lime application to Halfmoon Lake, mean winter total phosphorus release rates (TPRR) decreased to 〈 1 mg m–2 day–1 compared with 3.6 mg m–2 day–1 during the winter after initial treatment. In the final year of lime application, mean summer TPRR decreased to 4.5 mg m–2 day–1 compared with 7.6 mg m–2 day–1 in the pre-treatment year.4. Mean macrophyte biomass declined and species composition was altered at 1 and 2 m depths in Figure Eight Lake during lime application. Over the first 6 years of treatment, macrophyte biomass at 2 m declined by 95% compared with concentrations recorded during the initial treatment year. In the last year of the study, macrophyte biomass at 2 m reached initial treatment concentrations, which coincided with the greatest water transparency. Over the treatment period, macrophyte species shifted from floating to rooted plants.5. Multiple lime applications can improve water quality in eutrophic hardwater lakes for periods of up to 7 years.

Notes: 1. Aquatic macrophytes are abundant in ponds and canals that are constructed in semi-arid regions for water storage and conveyance, as well as in lakes that are culturally enriched.2. Addition of Ca(OH)2 to two hardwater ponds at 250 or 275 mg L–1 caused an immediate eradication of submersed aquatic plants. Although these ponds are well-buffered (alkalinity: 2.57–3.94 mequiv L–1; pH: 8.1–9.0), lime addition caused an immediate increase in pH of 0.2–3 units.3. Application of 135 mg L–1 Ca(OH)2 for 24 h or 210 mg L–1 Ca(OH)2 for 65 h to two irrigation canals had no effect on macrophyte biomass at the lower concentration and duration, but resulted in the elimination of aquatic macrophytes 1 month after the higher concentration, longer duration treatment.4. Unlike the macrophyte control achieved following application of 210–275 mg L–1 Ca(OH)2 to ponds or canals, microcosm experiments in which lime formulation [slaked lime (Ca(OH)2), calcite (CaCO3), or a 1 : 1 mixture] and concentrations (up to 1500 mg L–1) were manipulated failed to elicit a consistent change in macrophyte biomass. Macrophytes in microcosms treated for the short-term (23–33 days) with ≥ 200 mg L–1 Ca(OH)2 or a mixed Ca(OH)2/CaCO3 formulation always lost pigmentation, but biomass was not consistently reduced.5. Declines in macrophyte biomass following treatment of ponds and canals may have been triggered by a short-term rise in pH which, in these relatively warm (22–23 °C) alkaline (2.28–3.94 mequiv L–1) systems, would have resulted in low concentrations of free CO2 and bicarbonate for photosynthesis.

Notes: 1. To assess changes in stoichiometric constraints on stream benthos, we measured elemental composition of epilithon and benthic macroinvertebrates in intrinsically P-limited mountain rivers, upstream and downstream of low-level anthropogenic nutrient enrichment by effluents of municipal wastewater treatment plants.2. While there was a broad range in the elemental composition of epilithon (C : P ratios of 200–16 500, C : N ratios of 8–280, N : P ratios of 8–535) and heptageniid mayfly scrapers (C : P ratios of 125–300, C : N ratios of 5.1–7.2, N : P ratios of 20–60), the average C : P ratio of epilithon was 10-fold lower and the average C : N ratio twofold lower at more nutrient-rich downstream sites. Nutrient ratios in benthic macroinvertebrates were lower than in epilithon and varied little between relatively nutrient-poor and nutrient-rich sites.3. We modified the existing definition of producer-consumer elemental imbalance to allow for variation in consumer nutrient content. We defined this ‘non-homeostatic’ imbalance as the perpendicular distance between the producer and consumer C : P, C : N, or N : P ratios, and the 1 : 1 line.4. At P-limited sites, the estimated mayfly N : P recycling ratio was higher than the N : P ratio in epilithon, suggesting nutrient recycling by consumers could accentuate P-limitation of epilithon.5. Measuring the degree of producer–consumer nutrient imbalance may be important in predicting the magnitude of effects from nutrient enrichment and can help elucidate the causes and consequences of ecological patterns and processes in rivers.

Notes: SUMMARY. 1. The impact of crayfish on the biomass, density and shoot morphology of four submersed plant species was examined under semi-natural conditions. Male or female crayfish (Orconectes virilis) were held for 5 weeks at biomasses of 0, 5, 10 or 18 g m−2 (live weight) in twelve plastic pools (4.67 m2, surface area) containing Potamogeton richardsonii, Myriophyllum exalbescens, Nuphar variegatum and Sparganium eurycarpum.2. Crayfish significantly affected biomass, density and/or shoot morphology of all four macrophyte species. Differences in the effect of crayfish on macrophyte growth were related to plant species, crayfish sex and activity, and the abundance of alternative foods.3. The effect of female crayfish on macrophyte growth was generally stimulatory. Myriophyllum and Potamogeton biomass, Potamogeton density and Myriophyllum length increased in the presence of female crayfish, possibly due to the reduction in herbivorous snails as a result of crayfish predation. In contrast, plant growth decreased in the presence of male crayfish: Myriophyllum, Nuphar and Potamogeton biomass, Myriophyllum and Sparganium density, and Sparganium and Poiamogeton length were reduced at male crayfish biomasses between 5 and 18 g m−2.4. These results indicate that even relatively low densities of crayfish can greatly affect the growth of submersed aquatic plants. Because of their ability to modify aquatic macrophyte, macroinvertebrate and, ultimately, fish communities, the introduction of crayfish into lakes where they do not occur could have a major effect on the structure and composition of the littoral zone.

Notes: SUMMARY. 1. The impact of crayfish predation on the abundance of macroinvertebrates was examined under semi-natural conditions. Female (Experiment 1) or male (Experiment 2) crayfish (Orconectes virilis) were held for 5 weeks in twelve small pools (4.67 m2 surface area) at biomasses of 0. 5, 10 or 18 g m−2 (live weight). The pools were stocked with known densities of macroinvertebrates.2. Crayfish significantly affected the abundance of macroinvertebrates in the pools. Differences in the effects of crayfish on macroinvertebrates were related to crayfish sex, the presence of age-0 crayfish, and the species of macroinvertebrate.3. The abundance of snails (Stagnicola elodes and Physa gyrina) was greatly reduced, in comparison with controls, by biomass of female crayfish ≥10 g m−2 and by biomasses of male crayfish ≥5 g m−2. The total density of non-molluscan invertebrates was inversely correlated with the biomass of female crayfish but the total biomass of non-molluscan invertebrates did not differ between treatments. This is consistent with our observation that small invertebrates (〈2 mg wet weight) were less numerous, and large amphipods (32–64 mg) were more numerous, in pools stocked with female crayfish. In contrast, male crayfish had little apparent effect on the abundance of non-molluscan invertebrates.4. Age-0 crayfish hatched at the end of Experiment 1 and were present in each pool at the start of Experiment 2. Surprisingly, male crayfish preyed little on age-0 crayfish. At the end of Experiment 2, the densities of age-0 crayfish varied between six and 116 individuals m−2 and there was a strong inverse correlation between the mean biomass and density of age-0 crayfish recovered from the pools. This suggests age-0 crayfish were food limited in the pools and may explain the dominance of oligochaetes (which largely escape predation by burrowing) in the invertebrate community at the end of Experiment 2.5. These results indicate that even relatively low densities of crayfish could greatly affect the abundance of macroinvertebrates in lakes. The introduction of crayfish into lakes (most lakes in Alberta currently have no crayfish) could substantially affect abundance and species composition of the macroinvertebrate community and, ultimately, the fish populations.