Nutrients in lakes

productivity in lakes.

. shows a pervasive role for nutrients.

Like streams, lakes receive nutrients by the weathering of rocks and soils in their catchment areas, in the rainfall and as a result of human activity (fertilizers and sewage input). They vary considerably in nutrient availability. A study of 12 Canadian lakes shows a clear relationship between gross primary productivity (GPP) and phosphorus concentration and demonstrates the importance of nutrients in limiting lake productivity (Figure 17.15). Note that GPP easily exceeded ecosystem respiration in most lakes, emphasizing the overriding importance of autochthonous production in these lakes. The outlier in the top right corner of Figure 17.15b was atypical of the study sites because it received sewage effluent; here the allochthonous input of organic matter led to a higher consumption than production of organic carbon in the lake.

Productivity Lake

Figure 17.14 (a) Photosynthetically active radiation (PAR) reaching the bed of a Tennessee stream (bars) and stream water nitrate concentration (circles) during the spring of 1992 (the patterns were very similar in 1993). (b) Gross primary productivity in the stream during the spring in 1992 and 1993 (calculated on the basis of whole stream diurnal changes in oxygen concentration). (After Hill et al., 2001.)

Figure 17.14 (a) Photosynthetically active radiation (PAR) reaching the bed of a Tennessee stream (bars) and stream water nitrate concentration (circles) during the spring of 1992 (the patterns were very similar in 1993). (b) Gross primary productivity in the stream during the spring in 1992 and 1993 (calculated on the basis of whole stream diurnal changes in oxygen concentration). (After Hill et al., 2001.)

It is worth noting that the balance of radiant energy relative to the availability of key nutrients can affect C : N : P ratios (stoichiometry) in the tissues of primary producers. Thus, Sterner et al. (1997b) found in some phosphorus-deficient Canadian lakes that the availability of PAR relative to total phosphorus (PAR : TP) affected the balance of carbon fixation and phosphorus uptake in algal communities and, thereby, caused variations in C : P ratios in

... whose availability may interact with radiant energy to affect algal 'stoichiometry' (C : N : P ratios)

Figure 17.15 (a) Relationship between the gross primary productivity of phytoplankton (microscopic plants) in the open water of some Canadian lakes and phosphorus concentration. (b) The relationship between ecosystem respiration and gross photosynthesis measured on various dates in the study lakes. The dashed line shows where respiration equals GPP. The solid line shows the regression line for the relationship. Metabolic measurements were made in bottles in the laboratory at lake temperatures on depth-integrated water samples taken from the field. (After Carignan et al., 2000.)

Stoichiometry Plants

living algal cells and algal detritus. The zooplankton that consume live algae and the decomposers and detritivores that depend on algal detritus each have specific nutrient requirements, and these are very different from the nutrient ratios in algae. Thus, the changes in algal stoichiometry noted by Sterner et al. have consequences for heterotrophic metabolism and productivity. We consider elsewhere how such imbalances between the stoichiometry of plant tissue and of its consumers affect food web interactions, decomposition and nutrient cycling (see Sections 11.2.4, 17.5.4 and 18.2.5).

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Responses

  • mathias
    How nutrients affect the productivity of a lake?
    3 years ago

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