The safe disposal of human excreta is of paramount importance for the health and welfare of populations living in low income countries as well as the prevention of pollution to the surrounding environment. On-site sanitation (OSS) systems are the most numerous means of treating excreta in low income countries, these facilities aim at treating human waste at source and can provide a hygienic and affordable method of waste disposal. However, current OSS systems need improvement and require further research and development. Development of OSS facilities that treat excreta at, or close to, its source require knowledge of the waste stream entering the system. Data regarding the generation rate and the chemical and physical composition of fresh feces and urine was collected from the medical literature as well as the treatability sector. The data were summarized and statistical analysis was used to quantify the major factors that were a significant cause of variability. The impact of this data on biological processes, thermal processes, physical separators, and chemical processes was then assessed. Results showed that the median fecal wet mass production was 128 g/cap/day, with a median dry mass of 29 g/cap/day. Fecal output in healthy individuals was 1.20 defecations per 24 hr period and the main factor affecting fecal mass was the fiber intake of the population. Fecal wet mass values were increased by a factor of 2 in low income countries (high fiber intakes) in comparison to values found in high income countries (low fiber intakes). Feces had a median pH of 6.64 and were composed of 74.6% water. Bacterial biomass is the major component (25–54% of dry solids) of the organic fraction of the feces. Undigested carbohydrate, fiber, protein, and fat comprise the remainder and the amounts depend on diet and diarrhea prevalence in the population. The inorganic component of the feces is primarily undigested dietary elements that also depend on dietary supply. Median urine generation rates were 1.42 L/cap/day with a dry solids content of 59 g/cap/day. Variation in the volume and composition of urine is caused by differences in physical exertion, environmental conditions, as well as water, salt, and high protein intakes. Urine has a pH 6.2 and contains the largest fractions of nitrogen, phosphorus, and potassium released from the body. The urinary excretion of nitrogen was significant (10.98 g/cap/day) with urea the most predominant constituent making up over 50% of total organic solids. The dietary intake of food and fluid is the major cause of variation in both the fecal and urine composition and these variables should always be considered if the generation rate, physical, and chemical composition of feces and urine is to be accurately predicted.

Transect measurements, continuous monitoring, and synoptic surveys were used to examine patterns in light availability, temperature, and dissolved oxygen concentrations within and outside emergent vegetation zones in Goose Lake Marsh. a natural prairie pothole wetland in central Iowa. Water column light availability was less than 2% of ambient light in emergent vegetated areas due to canopy cover, small floating plants (lemnids), and plant litter. Water temperatures and dissolved oxygen concentrations were significantly lower and varied less diurnally in vegetated areas. Three habitat zones could be identified based on patterns in vegetation and dissolved oxygen: (1) a zone of dense emergent macrophytes providing significant submerged structure but with nearly or completely anoxic water, (2) a transition zone of sparse emergent macrophytes providing less structure but with more aerobic water, and (3) an open water zone with consistently aerobic water but with little submerged structure. Vegetation patterns are likely to control major aspects of wetland biogeochemistry and trophic dynamics, and wetlands should be viewed as complex mosaics of habitats with distinct structural and functional characteristics.

The Northern Lakes and Forests ecoregion of Minnesota contains thousands of lakes, characterized by their sensitivity to acid rain and typically low productivity. Four acid-sensitive lakes were studied from 1988 to 1991 to determine if phytoplankton were deficient in nitrogen, phosphorus, or both N and P and if the nutrient input via atmospheric deposition could increase primary production. The relative accuracy of predictions based on growth response bioassays, physiological assays, and nutrient deficiency indices was also evaluated. Our results show that (1) N enrichment generally caused a greater biomass response than P, although N + P almost always yielded the greatest effect and co-limitation was likely in two of the lakes, (2) predictions based on DIN:TP ratios generally agreed with the growth bioassays; TN:TP and DIN:SRP were not useful and could be misleading, and (3) atmospheric deposition could satisfy most of the daily algal N demand and increase the fertility of these lakes. These results suggest that although water quality protection based solely on P may not protect against this non-point source of nutrients, without these control strategies, P inputs would be expected to have a disproportionately greater stimulation of phytoplankton growth.

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