quality, wetland and aquatic produc- 

 tivity, and increased salinity intrusion 

 (see ECOLOGICAL ISSUES). 



The Barataria hydrologic unit has 

 the second highest population (after the 

 Pontchartrain unit) in the study area 

 (Hopkinson 1978). This basin is bor- 

 dered by one of the world's largest 

 concentrations of chemical plants 

 (Hopkinson 1978) and has the largest 

 area of agricultural land of the seven 

 hydrologic units within the MDPR (14,000 

 ha, or 34,600 acres). Urban and agri- 

 cultural runoff, sewage, and some in- 

 dustrial wastes enter the wetland and 

 aquatic systems of the basin, where they 

 must be assimilated. 



The major impacts of human activ- 

 ities are the result of (1) eutrophica- 

 tion caused by increased nutrient 

 loading from urban and agricultural 

 areas; (2) wetland loss resulting from 

 river entrainment, land development, 

 canals, navigation channels, impound- 

 ments, salinity intrusion, subsidence 

 and sea level rise; and (3) toxic sub- 

 stances from wastewater plants, indus- 

 try, hazardous waste sites, agricultural 

 runoff (both fertilizers and herbi- 

 cides), and herbicides used on aquatic 

 weeds, especially water hyacinth. 



Eutrophication 



Eutrophication is the natural or 

 artificial addition of nutrients to 

 water bodies, and the effects of these 

 added nutrients on the ecosystem. Al- 

 though eutrophication may be a natural 

 process, it is often accelerated by 

 human activities. Eutrophication typi- 

 cally results in changes in water 

 quality and algal blooms, leading to the 

 establishment of undesirable species, 

 the destabilization of natural communi- 

 ties, and periodic anoxic (low oxygen) 

 conditions (Craig and Day 1977). 



Waters of the upper and mid basin 

 (Lac des Allemands and Lake Cataouatche) 

 are strongly eutrophic (Seaton and Day 

 1979). These conditions are linked to 

 increasing total runoff from upland 

 areas into basin waters. The concen- 

 tration of nutrients and suspended 



sediments in upland runoff, and the 

 total volume of runoff, are both in- 

 creasing because of the clearing of 

 forested land for agriculture and the 

 conversion of agricultural land to urban 

 and industrial uses. Urbanized area is 

 projected to almost double by 1995 

 (Hopkinson and Day 1980a). The rela- 

 tionship between upland runoff and 

 eutrophic conditions in the MDPR has 

 been demonstrated in a number of studies 

 (Day et al. 1977; Craig and Day 1977; 

 Hopkinson and Day 1979; Seaton and Day 

 1979; Stone 1980a). 



In addition to total nutrient 

 loading, canal density has been linked 

 to eutrophication, by directly shunting 

 agricultural and urban runoff from the 

 uplands into water bodies. In the past, 

 runoff from the natural levees flowed 

 slowly through wetlands before entering 

 Lac des Allemands and other water bodies 

 in the upper basin. The evidence for a 

 relationship between canals and reduced 

 water quality in the upper basin is 

 increasing. Canals consistently have 

 more turbid water than natural streams, 

 in addition to higher nutrient levels. 

 Gael and Hopkinson (1979) showed a 

 positive relationship between the den- 

 sity of canals and the trophic state (an 

 index of the degree of eutrophication) 

 of water bodies in the Barataria basin 

 (Figure 47). Kemp (1978) showed a 

 marked increase in the Nitrogen: 

 Phosphorus ratio of water flowing out of 

 drainage canals compared with water 

 flowing from swamps, especially after 

 heavy rains (Figure 48). A low N:P 

 ratio indicates that nitrogen is being 

 biologically removed from the water (in 

 this case by denitrif ication) . This 

 indicates that the swamp forest habitat 

 assimilates nitrogen and improves water 

 quality. 



Seaton and Day (1979) and Witzig 

 and Day (1982) developed a numerical 

 trophic state index (TSI) for the Bara- 

 taria basin, based on the data collected 

 over a 2-year period (Table 14). 



All stations with a positive index 

 were classified as eutrophic or hyper- 

 eutrophic. These stations were charac- 

 terized by relatively high chlorophyll, 



110 



