Implications For Lake Management Research Articles

Phosphorus Paradox Scarcityand Overabundance of a Key Nutrient

In between shepherding the United States through the Great Depression and bracing the country for war in Europe, then-President Franklin Roosevelt took a moment in 1938 to tell Congress about phosphorus.1 More specifically, he spoke about phosphates, the most commonly commercially exploited form of phosphorus. Roosevelt’s was not a scientific presentation but a cautious alert about the critical role this element plays in agricultural production. Private interests were exporting increasing amounts of the country’s phosphates to markets abroad, he warned. Given the prospect that this vital constituent of fertilizer could come into short supply domestically, Roosevelt recommended framing a formal policy to deal with a strategic issue. “The disposition of our phosphate deposits should be regarded as a national concern,” he said. “The situation appears to offer an opportunity for this nation to exercise foresight in the use of a great national resource heretofore almost unknown in our plans for the development of the nation.”1 In spite of Roosevelt’s call, no phosphate policy was forthcoming. More than seven decades on, the phrase “heretofore almost unknown” still echoes in many discussions about phosphorus. Meanwhile, the significance of phosphates is even more profound today than it was in the 1930s. Phosphate rock has emerged as a globally traded commodity linked to a diverse set of politically charged debates, ranging from environmental degradation and threats to human health to food security and agricultural sovereignty.

Spatial-Dynamic Modeling of Algal Biomass in Lake Erie: Relative Impacts of Dreissenid Mussels and Nutrient Loads

Over the past several decades, reductions in phytoplankton stocks and increased water clarity in Lake Erie have resulted from phosphorus load abatement and the introduction of zebra (Dreissena polymorpha) and quagga mussels (D. bugensis). The relative impacts of these developments and their implications for lake management have remained difficult to delineate. To address this issue, we numerically model the complex biophysical interactions occurring in Lake Erie using a two-dimensional hydrodynamic and water quality model that is extended to include dreissenid mussel and zooplankton algorithms. The model reasonably simulates longitudinal trends in water quality as well as the dynamics of central basin hypoxia. Phosphorus is the limiting nutrient through the euphotic zone and its control decreases the algal growth rate and biomass (∼55–60%). Filter feeding by dreissenid mussels also decreases algal biomass (∼25–30%), simultaneously stimulating increased net algae growth through enhanced algal consumption and subsequent phosphorus recycling. Effective recycling implies that algae stocks are ultimately regulated by external phosphorus loads. Returning phosphorus loads to pre-abatement 1960s levels, in the presence of dreissenid mussels, results in a western basin algae concentration of ∼0.7mgdryweightL−1 with a potential for nuisance algae growth.

Persistence and Remobilization of Arsenic in Massachusetts (USA) Lakes Treated With Arsenical Herbicides

From 1953 to 1969 the Commonwealth of Massachusetts funded a program to evaluate the effectiveness of sodium arsenite for treating algae and macrophytes in lakes. It is well known that arsenic (As) is persistent in the environment; however, little work has been done to determine its long-term fate in the treated lakes. Once sodium arsenite is added to lakes, As typically precipitates and accumulates in bottom sediments, but under certain conditions As in surface sediments can be remobilized to the water column under certain conditions. The goals of this study were to determine whether residual As is present in elevated concentrations in the surface sediments (top 0–15 cm) of treated lakes, and whether As is being significantly remobilized. Eleven lakes were studied: five were known to have been treated with sodium arsenite; three were suspected of having been treated; and three untreated lakes were used for reference. Surface sediment grab samples were collected at multiple locations in each lake and analyzed for total As. In addition, water samples were collected along a vertical transect at the deepest point in each lake and analyzed for total As. In three of the five treated lakes and one of the lakes suspected of having been treated, sediment As concentrations were >100 mg/kg, or about four-fold higher than background. Analysis of the water samples showed that As was being remobilized from sediments of both the treated and untreated lakes where reducing conditions existed. The highest concentrations of dissolved As were measured in the bottom waters of treated lakes at levels >100 μg/L, which is about 50-fold higher than background. Elevated As levels in the sediments of treated lakes could have implications for lake management.

The paleolimnological development of the twin lakes Etujärvi and Takajärvi in Askola, southern Finland - implications for lake management

The twin lakes Etujarvi and Takajarvi in Askola, southern Finland, are closely interconnected mesotrophic headwater lakes with a relatively small catchment area. Both of the lakes have suffered from eutrophication and its consequences. Remediation activities such as oxygenation and biomanipulation have not resolved the problems. In this study a large set of paleolimnological techniques (radiometric AMS dating, spherical carbonaceous particles analysis, sediment lithology, grain-size analysis, phosphorus fractionation, and diatom analysis) were applied to put together the development of the basin and its water level fl uctuations during the Holocene. The age for observed Trapa natans -horizons was determined, and lake management options were discussed. The studied lakes dried up after isolation from the Ancylus Lake at about 9500 cal. B.P. and remained at very low water level until ca. 8700–8500 cal. B.P. The mid-Holocene rise in water level resulted in fl uctuating water levels, and led to the most recent rise starting about 2500 cal. B.P. as wet and cool climate conditions prevailed. The pronounced water level fl uctuations led to the extensive growth of peat deposits surrounding the lake and probably also forced T. natans to disappear from lake fl ora. The unstable, erodable peat rims impact the lakes, causing heavy load of humic substances to the lake and presenting additional deterioration to their recreational value.

Cylindrospermopsis racihorskii in Three Central Florida Lakes: Population Dynamics, Controls, and Management Implications

ABSTRACT Cylindrospermopsis racihorskii is a potentially toxic cyanobacterium that has begun appearing, or alternatively, increasing, and has come to dominate some Florida water bodies. C. racihorskii began exponentially increasing in Lake Jesup, Florida around 1997. As a result, the phytoplankton community in the lake has declined in terms of species richness and diversity. Compared to other lakes in the region this species is still maintaining relatively dynamic population cycles in the lake. Lake stage appears to affect C. racihorskii differently than the aggregate phytoplankton community in Lake Jesup. Correlation analysis suggests that magnesium limitation, among other factors, may be an important factor influencing C. racihorskii growth in Lake Jesup, but appears absent in Lake Apopka and Lake Griffin. Finally, increases in C. racihorskii are associated with increases in phytoplankton biomass yield per unit phosphorus, having important implications for lake management and restoration.

Land use, sediment loads and dispersal pathways from two catchments at the southern end of Lake Tanganyika, Africa: implications for lake management

Increasing sediment loads entering the Lake Tanganyika ecosystem are hastening the need for improved understanding of the linkages between catchment characteristics and influent sediment transport and loading. Sediment loads of two catchments at the southern end of the lake were estimated for October 1998–December 1999, and catchment characteristics determined using GIS. It was found that both sediment yields and loads were higher from the catchment of the Lunzua River (19.8 t km−2 and 20,114 t, respectively) compared with that of the Kalambo (4.1 t km−2 and 12,197 t) in 1999. These differences were both attributed to the smaller size and higher road density of the Lunzua catchment, and suggest that previous recommendations regarding the positioning of underwater lake reserves fail to take into account the low sediment retention capacity of small mountainous rivers. Differences between the study rivers in the transport of suspended sediments, organic matter, and bedload sediments into the lake were also found, the latter determined by the novel application of the 'McLaren Model'.

Impact of light regimen and self‐shading by algal cells on primary productivity in the water column of a shallow tropical lake (Lake Naivasha, Kenya)

AbstractLight is the factor that fundamentally determines the level of primary production. Primary productivity is controlled by bottom‐up factors (nutrient levels), with secondary effects due to biological factors (zooplankton grazing). The light regimen experienced by algae is determined largely by mixing of the water column. The processes of photoinhibition and light attenuation combine with the resultant light–dark adaptation to shape the vertical productivity profile and it is important to determine their importance separately because they vary spatially and temporally. Daily variations in productivity can be as large as longer‐term changes and events causing high productivity may not be important in whole‐lake terms. At approximately 0.5 m depth, there is maximal photosynthesis causing depletion of nutrients, but there is vertical homogeneity in productivity control and horizontal similarity in productivity levels. There is zero productivity below 5 m depth due to light attenuation but, if the benthos becomes productive due to an environmental change, such as decreased turbidity, overall productivity may rise appreciably. Self‐shading was investigated by incubating serial dilutions of whole lakewater with filtered water to reduce the density of algal cells. Photosynthetic efficiency was calculated as productivity per unit of chlorophyll a. Self‐shading showed different responses for conditions of ‘low’ and ‘high’ productivity. With low productivity, there was a shading loss of 17%, while for high productivity this was 46%. Thus, self‐shading is seen to have a considerable impact on potential productivity and may affect phytoplankton–cyanobacterial community structure with implications for lake management.

Alternative stable states of macrophytes versus phytoplankton in two interconnected impoundments of the New Danube (Vienna, Austria)

Natural dynamic processes leading to a shift from algal to macrophyte domination in the two impoundments of the New Danube flood-relief channel are associated with and explained by a theory of bi-stable states. Changes are largely caused by alterations of water level and hence the retention times of the impoundments. Implications for water quality evaluation are discussed using the concept of potential water column concentrations of phosphorus. Calculations indicate the importance of macrophytes as structures that can buffer nutrient concentrations, via uptake and storage in plant tissues Results are contrasted with similar hut anthropogenically-induced forward and reverse shifts in the nearby Old Danube seepage lake, and implications for lake management are discussed.

Simultaneous Nitrogen and Phosphorus Deficiency in Natural Phytoplankton Assemblages: Theory, Empirical Evidence, and Implications for Lake Management

ABSTRACT There is considerable support in the ecological literature for the theory that phytoplankton communities experience non-equilibrium conditions. Therefore, it is possible that not all species of an algal community are deficient in the same nutrient, challenging the belief held by some aquatic scientists and lake managers that phosphorus is the universal nutrient limiting phytoplankton growth in lakes. Simultaneous additions of NH4 + and PO4 3− were necessary to stimulate community photosynthesis – uptake of 14CO2 – during summer stratification in a number of northern Rocky Mountain lakes and reservoirs, whereas adding one nutrient had no significant effect on community photosynthesis. However, size-fractionated bioassays showed that additions of nitrogen alone stimulated photosynthesis of specific size classes of phytoplankton in these systems. The authors' data have the following implications for lake management: (1) phosphorus should not be assumed to be the only nutrient controlling photosynthesis; (2) simultaneous enrichment of nitrogen and phosphorus may be necessary to measurably increase community photosynthesis, especially in nutrient dilute systems; and (3) adding NH4 + may cause changes in phytoplankton community structure without changing community primary production.

Factors Controlling Oxygen Depletion in Ice-Covered Lakes

Winter oxygen depletion rates from four sets of Canadian lakes (prairie, southeastern Ontario, Arctic, and Experimental Lakes Area) differing in morphometry and trophic state, were analyzed. An inverse relationship was found between oxygen depletion rate and mean depth. The effect of lake trophic status on oxygen depletion rate was demonstrable after the influence of basin morphometry was removed by regression of oxygen depletion rate against the sediment area: lake volume ratio. The sediments of eutrophic lakes consumed oxygen about 3 times faster (0.23 g∙m−2∙d−1) than those of oligotrophic lakes (0.08 g∙m−2∙d−1), but water column respiration was about the same (0.01 g∙m−3∙d−1) for both groups of lakes. Data from prairie lakes showed that the winter oxygen consumption was limited by oxygen supply below an average whole-lake oxygen concentration of 3.8 mg∙L−1. The rate of eddy diffusion near the sediments in ice-covered prairie lakes was 3.72 ± 1.41 × 10−3 cm2∙s−1. Implications for lake management during the winter are discussed.Key words: oxygen, depletion, respiration, lakes, ice-covered, winter, sediments, model, consumption

Eutrophication and Recovery in Experimental Lakes: Implications for Lake Management

Combinations of phosphorus, nitrogen, and carbon were added to several small lakes in northwestern Ontario, Canada, at rates similar to those in many culturally eutrophied lakes. Phosphate and nitrate caused rapid eutrophication. A similar result was obtained with phosphate, ammonia, and sucrose, but recovery was almost immediate when phosphate additions only were discontinued. When two basins of one lake were fertilized with equal amounts of nitrate and sucrose, and phosphorus was also added to one of the basins, the phosphateenriched basin quickly became highly eutrophic, while the basin receiving only nitrogen and carbon remained at prefertilization conditions. These results, and the high affinity of sediments for phosphorus indicate that rapid abatement of eutrophication may be expected to follow phosphorus control measures.