Macrophytes lakes

There is a further complication in shallow lakes containing macrophytes (aquatic flowering plants, pteridophytes, and macroalgae). These take up and accumulate nutrients from the water and from the aquatic soil in which they are rooted (sediment). Although these plants are sometimes classed as nuisance weeds, they nevertheless act as an important alternative sink for nutrients which are denied to the plankton. In recent times, a key role of macrophytes in the successful and sustained management of water quality has been identified and explained. ... 

McIntosh A.W., Shephard B.K., Mayes R.A., Atchison G.J., Nelson D.W. Some aspects of sediment distribution and macrophyte cycling of heavy metals in a contaminated lake. JEnvironQual 1978 7 301-305. 

Significant concentrations of cyanotoxins have been found to accumulate in the tissues of macroinvertebrates such as mollusks and crustaceans, presenting an indirect route of exposure for invertebrates, fish, and aquatic mammals at higher trophic levels (Negri and Jones 1995). In natural systems, mortality among benthic invertebrate herbivores is probably low because most bloom-forming bacteria are planktonic and only periodically come into contact with the benthos. Nevertheless, Kotak et al. (1996) determined that enhanced mortality of snails at the end of a bloom cycle in Canadian lakes was due to consumption of Microcystis cells that had formed a scum on the surface of macrophytes. Oberemm et al. (1999) found that aqueous microcystins, saxitoxins, and anatoxin-a all resulted in developmental delays in fish and salamander embryos. Interestingly, more severe malformations and enhanced mortality were observed when larvae were exposed to crude cyanobacterial extracts than to pure toxins applied at natural concentrations (Oberemm et al. 1999). 

FIGURE 3 Proportion of lake area accounted for by littoral zones for the world s lakes (a), and the proportion of extracellular (ER) dissolved organic matter inputs derived from littoral zones (b see text for description of the model). The solid lines illustrate relationships in which lake boundaries are restricted to littoral and pelagic zones and the dotted lines illustrate patterns in which lake boundaries are expanded to include adjacent wetlands. In (b), the two sets of lines illustrate the range in the contribution of littoral zones to total lake ER with variation in rates of primary production for phytoplankton (0.1-2.0 kg organic matter m-2 yr 1) and macrophytes (0.6-3.8 kg organic matter nT2 yr 1). The relationship between littoral zone area and number of lakes is from Wetzel (1983). 

This major input of DOM from macrophytes is not restricted to lakes, but is also realized in other aquatic ecosystems. DOM export from watersheds in lotic ecosystems is directly related to annual runoff, but significantly greater in swamp-draining streams compared with upland-draining streams (Mulholland and Kuenzler, 1979 see Chapter 2 and 6). In the Hudson Estuary, planktonic bacterial production is 3 to 6 times greater than primary production (Findlay et al., 1992). DOC derived from submerged aquatic plants in part supports the difference in bacterial carbon uptake and planktonic primary production. 

Wetzel, R. G. 1969. Factors influencing photosynthesis and excretion of dissolved organic matter by aquatic macrophytes in hard-water lakes. Verhandlungen der Internationale Vereiningung fur Theoretische und Angewandte Limnologie 17 72—85. 

Aquatic macrophytes living in lakes and rivers face strong competition with... 

In chapter 14, John Melack and Bruce Forsberg provide a quantitative assessment of the role of floodplain lakes in regional cycles of C, N, and P. Floodplain lakes were found to be important centers of organic carbon production and delivery to the river system. The combined primary production of macrophytes, forests, periphyton, and plankton associated with floodplain lakes is estimated at 117 Tg C yri, of which only 24% is remineralized in the lakes. As a result, an estimated 90 Tg C yr are delivered to the river system by continual and seasonal exchanges. This input alone amounts to... 

Large expanses of floating macrophytes develop and decay each year on the flood-plain of the central Amazon basin 0unk 1970 1997). Herbaceous macrophytes are especially abundant in lakes associated with whitewater rivers, where nutrient-rich sediments and waters stimulate their development. A seasonal succession of herbaceous plant communities occurs in lakes as the ATT2 expands and shrinks in synchrony with... 

The seasonally changing biomass of floating macrophytes was determined at Lake Calado with a combination of sampling and airborne videography (Fisher and Moline 1992 T.R. Fisher, personal communication Fig. 14.7). Further analysis of these data... 

---