Nutrient Cycling In Lakes Research Articles

Chara beds acting as nutrient sinks in shallow lakes—a review

The capability of Chara beds to act as nutrient sinks in shallow lakes is reviewed. Under favorable conditions charophytes form dense meadows. Biomass and nutrient content in such beds are comparable or even higher than in beds of vascular aquatic macrophytes. As some Chara species are capable of overwintering, the nutrient storage in plant biomass may extend beyond the growing season. Some commonly observed phenomena in vascular plants (nutrient uptake and mobilization of nutrients from the sediment) appear to be unlikely or negligible in Characeae. Charophytes have been reported to decompose slower than their vascular counterparts prolonging nutrient storage in plant biomass. Charophytes may also indirectly affect nutrient cycling in lakes. Utilization of bicarbonate is accompanied by precipitation of calcite during periods of intensive photosynthesis, favoring immobilization of P by binding in the crystal structure or sorption on sedimenting mineral particles. Charophytes are able to deliver oxygen to the sediment, thus potentially enhancing nitrification/denitrification processes and preventing iron-bound sediment phosphorus from being released to the overlying water. Furthermore, dense Chara meadows restrict sediment resuspension, consequently blocking an important internal source of nutrients to planktonic algae. We conclude that Chara meadows probably are an efficient nutrient trap in shallow lakes.

Alteration of Nutrient Cycles and Algal Production Resulting from Fish Introductions intoMountain Lakes

The introduction of salmonid fishes into naturally fishless lakes represents one of the most prevalent environmental modifications of aquatic ecosystems in western North America. Introduced fish may alter lake nutrient cycles and primary production, but the magnitude and variation of these effects have not been fully explored. We used bioenergetics modeling to estimate the contributions of stocked trout to phosphorus (P) cycles across a wide range of fish densities in lakes of the Sierra Nevada, California. We also assessed the larger effects of fish-induced changes in phosphorus cycling on primary production using paleolimnological analyses from lakes in the southern Canadian Rockies. Our analyses showed that total P recycling by fish was independent of fish density but positively related to fish biomass in the Sierra Nevada. In lakes with fish populations maintained by continued stocking, fish recycled P at over twice the rate of those in lakes where introduced fish populations are maintained by natural reproduction and stocking has been discontinued. We estimate that P regeneration by introduced fishes is approximately equivalent to atmospheric P deposition to these lakes. Paleolimnological analyses indicated that algal production increased substantially following trout introductions to Rocky Mountain lakes and was maintained for the duration of fish presence. The results of our modeling and paleolimnological analyses indicate that introduced trout fundamentally alter nutrient cycles and stimulate primary production by accessing benthic P sources that are not normally available to pelagic communities in oligotrophic mountain lakes. These effects pose a difficult challenge for managers charged with balancing the demand for recreational fisheries with the need to maintain natural ecosystem processes.

Mini-Review: Nutrient Cycling in Lakes and Streams: Insights from a Comparative Analysis

Understanding of general ecosystem principles may be improved by comparing disparate ecosystems. We compared nutrient cycling in lakes and streams to evaluate whether contrasts in hydrologic properties lead to different controls and different rates of internal nutrient cycling. Our primary focus was nutrient cycling that results in increased productivity, so we quantified nutrient cycling by defining the recycling ratio (ρ) as the number of times a nutrient molecule is sequestered by producers before export. An analytic model of nutrient cycling predicted that in lakes ρ is governed by the processes that promote the mineralization and retard the sedimentation of particulate-bound nutrients, whereas in streams, ρ is governed by processes that promote the uptake and retard the export of dissolved nutrients. These differences were the consequence of contrast between lakes and streams in the mass-specific export rates (mass exported · standing stock-1· time-1) of dissolved and particulate nutrients. Although ρ is calculated from readily measured ecosystem variables, we found very few published data sets that provided the necessary data for a given ecosystem. We calculated and compared ρ in two well-studied P-limited ecosystems, Peter Lake and West Fork Walker Branch (WFWB). When ecosystems were scaled so that water residence time was equal between these two ecosystems, ρ was three orders of magnitude greater in WFWB. However, when we scaled by P residence time, ρ was nearly equal between these two ecosystems. This suggests broad similarities in ρ across ecosystem types when ecosystem boundaries are defined so that turnover times of limiting nutrients are the same.

Phosphorus Loading of an Urban Lake by Bird Droppings

ABSTRACT The role of birds in nutrient cycling in lakes and reservoirs is often not quantified, or thought to be relatively unimportant. However, when bird populations are large relative to the size or volume of the waterbody, a substantial fraction of the nutrient pool may cycle through birds. In this report, we estimate the mass of phosphorus in bird droppings cycling through Green Lake, a productive lake in urban Seattle, between January 1992 and December 1994. Phosphorus loading from bird droppings is compared to the mass of phosphorus entering the lake from other sources measured during a concurrent limnologic study. Waterbirds spent 528,355 bird-days (the number of bird-use days) at Green Lake in 1992, 530,318 bird-days in 1993, and 546,943 bird-days in 1994. The most abundant bird species at the lake were American coots, mallards, gadwalls, and various species of gulls. Of all birds at Green Lake, waterbirds accounted for greater than 99% of the phosphorus loading. Total phosphorus loading by birds...

NUTRIENTS IN AFRICAN LAKE ECOSYSTEMS: DO WE KNOW ALL?

SUMMARY It is nearly sixty years since the first studies were undertaken on the nutrient chemistry of African lakes. There have been numerous studies on the chemical composition of African waters in the intervening years. Yet as recently as five years ago it was stated that little was known about nutrient cycling in lakes. Nutrient ‘species’ simply formed an additional list compiled along with lists of species of algae, zooplankton, aquatic plants and fish. A spate of monographs, papers and reports in recent years, however, has begun to fill some of the gaps in our knowledge of nutrient cycling in African lake ecosystems. This paper reviews the recent literature of nutrients in African lakes from the point of view of nutrient sources, in-lake nutrient kinetics and nutrient sinks, with particular reference to nitrogen and phosphorus, and their cycling rates into and out of various biotic and abiotic compartments. The principle conclusions that can be drawn from the review are as follows: Allochthonous inpu...