Freshwater Terrestrial Ecosystems

The dominant processes controlling the movements of P through terrestrial ecosystems are schematically presented in Fig. 14-4. In a general way, the overall movement of P on the continents may be envisioned as the constant erosion of P from continental rocks and transport in both dissolved and particulate form by rivers to the ocean, stopping occasionally along this pathway to interact with biological and mineral-ogical systems. 

Physical and chemical erosion of continental rocks, represented by the arrow labeled 1 on Fig. 14-4, introduces particulate and dissolved P to the soil system. The majority (90%) of the P eroded from rocks remains trapped in the mineral lattices of the particulate matter. This P will be transported with the suspended material or bedload downstream until it eventually reaches the estuaries and the oceans, never having entered the biological cycles. The small proportion of the P that is leached from the minerals into solution, however, is readily available to enter biological cycles (2) and to react with inorganic soil particles (3). 

Dissolved P in groundwaters is, of course, taken up by plants. Although many elements are required for plant life, in many ecosystems P is the least 

Lakes (4) also constitute an important component of the terrestrial P system. Because much of mankind s activities occur on or adjacent to lakes and because P availability has such a major influence on the biological community, P cycling in lakes has been studied extensively. The importance of understanding the transport of P through the lake system may be demonstrated by considering the hypo- 

As cooling occurs in the late fall and early winter, the thermal stratification breaks down, permitting mixing of the deep and surface layers. This allows the surface layers to be replenished with P. During the winter months, biological productivity in a temperate lake is limited by the availability of light rather than nutrients. 

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Lerman et al. (1975) considered several cases in which mankind s activities perturbed the natural cycle. If we assume that all mined P is supplied to the land as fertilizer and that all of this P is incorporated into land biota, the mass of the land biota will increase by 20%. This amount is small relative to the P stored in the land reservoir. Since P incorporated into land biota must first decompose and be returned to the land reservoir before being transported further, there is essentially no change in the other reservoirs. Thus, although such inputs would significantly alter the freshwater-terrestrial ecosystem locally where the P release is concentrated, the global cycle would be essentially unaffected. 

Disturbance of Phosphorus Biogeochemical Cycle in Agrolandscapes Conceptual ideas behind simulation of P cycling are related to construction of models for freshwater terrestrial ecosystems and a generalized oceanic system and understanding the restrictions of its application. 

This book has identified the most useful indicators of environmental changes in mercury contamination in 4 compartments of the environment 1) airsheds and watersheds, 2) water and sediment, 3) aquatic organisms (with emphasis on freshwater ecosystems), and 4) wildlife that live in freshwater, terrestrial, and/or coastal ecosystems. The indicators identified in this book are wide-ranging and involve measurements made at several different scales of time and space. The authors believe that these indicators will provide the best information to policymakers, as well as other stakeholders, as to whether environmental concentrations are changing (A indicators) and what the reasons for those changes might be (B indicators). 

The accident at the Chernobyl, Ukraine, nuclear reactor on April 26, 1986, contaminated much of the northern hemisphere, especially Europe, by releasing large amounts of radiocesium-137 and other radionuclides into the environment. In the immediate vicinity of Chernobyl at least 30 people died, more than 115,000 others were evacuated, and the consumption of locally produced milk and other foods was banned because of radiocontamination. The most sensitive local ecosystems were the soil fauna and pine forest communities. Elsewhere, fallout from Chernobyl measurably contaminated freshwater, marine, and terrestrial ecosystems, including flesh and milk of domestic livestock. Reindeer (Rangifer tarandus) calves in Norway showed an increasing frequency of chromosomal aberrations that seemed to correlate with cesium-137 tissue concentrations tissue concentrations, in turn, were related to cesium-137 in lichens, an efficient absorber of airborne particles containing radiocesium and the main food source of reindeer during winter. A pattern similar to that of reindeer was documented in moose (Alces) in Scandinavia. 

Within the defined areas, critical loads are calculated for all major combinations of tree species and soil types (receptors) in the case of terrestrial ecosystems, or water biota (including fish species) and water types in case of freshwater ecosystems. 

Table 7 Examples of the contribution of dissimilatory nitrate reduction to ammonium (DNRA) to total dissimulatory nitrate reduction in various freshwater, marine, and terrestrial ecosystems. The ranges are inclusive of aU sites and treatments reported for which appropriate data could be drawn, including those that manipulated...

Surface freshwater ecosystems consist of wetlands (e.g., bogs, fens, marshes, swamps, prairie potholes, etc.), streams, lakes (and artificial reservoirs), and rivers. Surface freshwater ecosystems receive most of their Nr from their associated watersheds, from atmospheric deposition, and from BNF within the system. There is hmited potential for Nr to accumulate within surface-water ecosystems, because the residence time of Nr within surface waters, like the water itself, is very brief. Residence times may be relatively longer in the sediments associated with wetlands and some larger lakes but are still short when compared to terrestrial ecosystems or the oceans. 

The role of the atmosphere in the phosphorus cycle seems to be poorly understood. Since it does not exist in the form of stable gaseous compounds, phosphorus in the atmosphere is either adsorbed on particulate matter, e.g. dust (including pollen) and exhaust fumes or dissolved in sea-spray. The fallout of phosphorus, as dry deposition and precipitation, has been estimated to be within the range 3.6—9.2 Tg P y for terrestrial ecosystems, 0.054— 0.140 Tg P y for freshwater ecosystems, and 2.6—3.5 Tg y" for the marine ecosystem. This gives a total fallout from the atmosphere of 6.3—12.8 Tg P y i (Pierrou, 1976). It should be noted, however, that Emery et al. (1955)... 

Research on the effect of climate on recovery of freshwaters is of direct interest in formulating new policy goals with respect to emissions of S and N compounds. Here the major research challenge is still the link between the C and N cycles in terrestrial ecosystems and how N deposition and global change will affect these cycles in the future. 

Beaune B, Muir D, Demaech B, Gamberg M, Poole K, Currie R, Dodd M, Duschenko W, Eamee ), Elkin B, Evans M, Grundy S, Hebert C, (OHNSTONE R, Kidd K, Koenig B, Lockhart L, Marshall H, Reimer K, Sanderson ) and Shutt L (1999) Spatial and temporal trends of contaminants in Canadian Arctic freshwater and terrestrial ecosystems a review. Sci Total Environ 230 145-207... 

Information on authorized and accidental releases of Tc to terrestrial ecosystems or to freshwater drainage systems from large reprocessing facilities in the former USSR, e.g., Chelyabinsk (Ma-yak PA), Krasnoyarsk (KMCIC), or Tomsk (SCC) is not available. However, significant amovmt of Tc have been identified in ground water and artificial reservoirs associated with Techa River in the close vicinity of the Mayak PA. 

Initially, effects to freshwater systems attributed, at least in part, to acid deposition were reported from Sweden, Norway and Canada. Now, however, effects are reported for both freshwater and terrestrial components of ecosystems in a large number of nations. Acid deposition may be considered an additional stress factor for terrestrial systems. Materials of technical, economic and cultural importance are also at risk from acid deposition. The immediate importance of these problems tends to indicate that the phenomenon of acid deposition is of recent origin, however, the subject has a relatively long history. As early as 1852 R. A. Smith collected and analysed rainwater in north west England, neologised the term acid rain and described its effects upon terrestrial ecosystems and materials. At this time, sulphur was the major pollutant and the effects of acid deposition were most clearly experienced at the meso scale. 

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