Trophic state

The residence time is very low, less than 1 month [36], and it can even attain 5 days during high flows [38]. The trophic state of the reservoir can change from year to year, from mesotrophic conditions [36, 40] to eutrophic ones [38, 39]. 

Dodds WK, Jones JR, Welch EB (1998) Suggested classification of stream trophic state distributions of temperate stream types by chlorophyll, total nitrogen, and phosphorus. Water Res 32 1455-1462... 

An example of a CCA biplot is shown in Figure 6. It was developed to explore the relationships between trophic state, several water chemistry... 

Figure 6. Canonical correspondence analysis for surface sediments of 41 lakes in British Columbia, Canada, that encompass a broad range of trophic states. Circles represent lakes and triangles represent the 25 most abundant diatom taxa. Arrows indicate environmental variables that correlate most strongly with the distribution of diatom taxa and lake-water chemistry, as detected by forward selection. Maximum depth (Zntax) and total phosphorus (TP) were transformed by using the In (x + 1) function. This analysis is discussed in detail in reference 46.

Another statistical issue is the relationship between the composition in the calibration set used to derive the transfer functions and the lakes for which the transfer functions will be applied. Calibration data sets should be modified if used to reconstruct chemistry of different types of lakes. A subset of calibration lakes can be selected that does not contain lakes so different that they might unduly influence optimum environmental values for a taxon (for example, saline lakes can be removed from a calibration data set to be used for generating data to infer trophic-state change in low-conductivity lakes). 

A crucial difference between aquatic and terrestrial ecosystems is that N additions do not commonly stimulate growth in aquatic systems, as seems to be the case in many terrestrial systems. N limitation may be the exception in aquatic systems rather than the rule. The question of whether N limitation is a common occurrence in surface waters will play a large role in determining whether N deposition affects the trophic state of aquatic ecosystems. 

Primary production (trophic state) affects S retention and speciation in several ways. As primary production increases, inputs of organic S to sediments in seston increase. Hence, as the organic carbon content of sediments increases, S content would be expected to increase proportionally. Such a simple relationship is not observed among nearly 80 lakes for which sediment S and C content are available (Figure IB). However, a line defining the minimum S content does increase linearly with increasing carbon content. The slope of this line corresponds to the mean C S ratio measured in seston... 

The CRS AVS ratio reflects the trophic state of a lake (cf. Urban (28), Table V). This observation may be explained by the preceding kinetic considerations. The high organic matter supply in eutrophic lakes leads to an intensive mineralization rate by both iron- and sulfate-reducing bacteria. However, reoxidation of Fe2+ to ferric oxide or of sulfide to sulfate does not take place because an anoxic hypolimnion prevents penetration of oxygen. Therefore FeS can build up, but the sediment becomes depleted with respect to reactive iron. 

Schmid, H., Bauer, F., and Stich, H.B. (1998) Determination of algal biomass with HPLC pigment analysis from lakes of different trophic state in comparison to microscopically measured biomass. J. Plankton Res. 20, 1651-1661. 

Trophic state can be measured directly via indicators of phytoplankton biomass and nutrient concentrations or indirectly by measuring water transparency (Table 1). Water transparency can be an accurate indicator of phytoplankton productivity, even though it is affected by nonbio-logical particles suspended in the water column. Secchi disk depth is the oldest, simplest, and quickest quantitative measure of water clarity. A Secchi disk is a black and white disk that is... 

Because an increased supply of nitrogen in marine waters and/or phosphorus in freshwaters is typically responsible for eutrophication, directly measuring the concentration of these nutrients can indicate trophic state. Nutrients in water are either dissolved or bound to particulates produced in situ and deposited into water bodies from groundwater, atmospheric deposition, and drainage basin runoff. To measure trophic state, nutrient concentrations are measured in samples... 

For the NJDEP (New Jersey Department of Environmental Protection NJDEP, 2007 Poretti and Franken, 2008) 40 lakes are sampled 3 times per year (spring, summer and fall). The trophic status of the 40 lakes was determined on the basis of Carlson s Trophic State Index (TSI), linked to TP, transparency and levels of chlorophyll-a ... 

The TSI measurement is largely used in the US as included in field protocols and daily operations for crews to use in the Survey of the Nation s Lakes (USEPA, 2007b). This aggregated method allows the lakes to be classified according to their trophic state. 

Figure 2.4.9 Relation between UV spectra (path-length 10 mm) and trophic state of lakes...

The given examples presented in this section illustrated the potential of UV spectrophotometry for improving information on the quality of water bodies and highlighted the perspectives of their integration on new approaches on water management. The portable instrument is in particular useful for the spatial and temporal water quality survey (river basin, lake...) based on measurements of some well-known physico-chemical parameters (TSS, TOC, COD, BOD, NO3-, surfactants). Nevertheless, the UV spectrophotometry and the suitable software developed to enhance the deconvolution of UV spectra allows to propose others applications, in particular qualitative interpretation in order to assess, for example, the trophic states of lakes. 

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