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studies not only in Dar es Salaam, Tanga and Zanzibar, where only a very limited area has been covered, but also in other parts of Tanzania where virtually no information on this subject exists.
2.6.2 Subject coverage
Most of the studies reported in the various papers and reports covered the area of pollution, mainly that emanating from sewage. Fewer studies have looked at other sources of water quality degradation and their impacts on the
natural environment and on human health. Consequently, there are reports on nutrient loads and distribution, BOD levels and coliforms. Studies on heavy metal pollution and that emanating from organic compounds and
agrochemicals are few and far between. These include a study by Mmochi and Mberek 1998 on pesticide pollution and those by Machiwa 1992a,b which assessed pollutionby heavy metals and toxic material.
Moreover, there are only few studies that have looked at the effects of pollutants, on the water quality in Tanzania. A good example is a report by Munisi 1998 who discussed the results of a determination on the effects of
discharges from a fertiliser factory on intertidal floral communities in Tanga. Both Tanga and Dar es Salaam have relatively high concentrations of manufacturing concerns. Since few industries in Tanzania treat their wastes
before they are discharged into the environment, it is obvious that they are principal sources of industrial pollution in the country. Given the current pace of industrial development in the country and the fact that only few studies
on industrial pollution have been done, it is important that more studies should be carried out to generate both baseline information as well as to follow trends on the impact of these wastes on the water quality.
2.6.3 Duration of studies longshort
A great majority of the studies are of short duration. Given that most of the studies reported in this review were carried out by students either on short weeks study programs or on field attachments, invariably the studies
tended to be very short. Where researchers did the studies, the duration of the studies was determined by the amount and source of funding. For obvious reasons, studies for Masters and PhD theses tended to be
comparatively longer than, for example, undergraduate reports and degrees. Similarly, studies that aimed to monitor long- term effects of a contaminant on the environment were longer than the average consultancy report.
On the whole though, long term studies were very rare.
From the above discussion it is obvious that specific efforts need to be taken to address the issue of time frame for sampling. It is important to identify which aspects or parameters that deserve to be addressed through long term
and which through short-term studies. The question of seasonality is also important. In Tanzania, seasonality is intrinsically linked to study duration. The annual weather cycle in the east African coastal areas is generally made
upof two periods of rainfall alternating with periods of dry weather. This cycle is essentially driven by the monsoon winds. Conceivably, this weather pattern has a large influence not only on waste discharges including
that from upland agricultural areas but also on dispersal patterns along the coast. Few studies that looked at temporal patterns are available. Consequently, temporal variationseasonality studies should be carried out when
addressing both agricultural as well as municipal waste discharges. Such studies are also important when assessing waste dispersal patterns and their effect on the biota.
Point source discharges are inherently long-term events. They are therefore ideally examined through long-term studies. Long-term studies over one or two years are also essential when one requires basic data to help prepare
a model of waste discharge and dispersion patterns. Long-term data therefore affords predictive capability.
2.6.4 Age of studies
