River input studies using continuous-series microecosystems.




Cooper, David C.

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The University of Texas, Marine Science Institute at Port Aransas


A group of six continuous-series microecosystems were constructed to simulate hydrological factors of estuarine regions. Exhanges and retention characteristics were adjusted to closely model the hydrological conditions of Trinity Bay, Texas. The responces of microecosystems to quantitative and qualitative changes in freshwater input were investigated. Due to fundatmental similarieis of all living systems, these responses might be especially representative of those which would occur in Trinity Bay if subjected to similar conditions; actual testing of this conjecture was logistically and operationally infeasible. Magnitude of primary production and community respiration in the freshwater protions of the microecosystems were dependent on both quantity and quality of freshwater input. Magnitudes of pirmary production and community respiration in the saltwater portions of the microecosystems were virtually independent of the quality and quantity of freshwater input. The metabolism of the freshwater portions of the microecosystems was hetertrophic under conditions of 60 dya freshwater retention time and autotrophic under conditions of infinite freswater retention time. Addition of an industrial effluen to the freshwater inputs resulted in extensive shifts toward metabolic hetertrophy b the more freshwater portions of the microecosystems. The metabolism of the saltwater cell postions was heterotrophic under all conditions of freshwater input. The communities of the freshwater portions of the microecosystems adapted to a dependency on allochtanous materials for productiona nd respiratory maintenance. The retardation of freshwater input resulted in larger portions of the nutrient pool within the systems being tied up on living components. The addition of industrial effluent increased the maintenance requirements of the communities. The retardation of freshwater input acted as an environmental stress abserved by all the freshwater portions of the microecosystems. Magnitudes of production and respiration were significantly lower, and zooplankton standing crops and species diversity decreased significantly. The addition of industrial effluent produced the same effects. There was a synergistic effect of reduced freshwater input and effluent loading on the freshwater portions of the microecosystems when the stresses on the receiving systems rendered the communities more susceptible to the imposition of the secondary stress. The organismal composition of the microecosystems was qualitatively similar but quantitatively dissimilar to the organizsmal compostion of Trinity Bay. Periphytonic flora gradually attained the dominant producer status, and were successionsal aftermath of planktonic floral dominance. Additional studies indicated that low level grazing by herbivores enhanced the primary productivity of the periphytonic flora; C02 enrichment enhaned primary production only in the freshwater portions of the microecosystems; and rates of production, repsiration, and zooplankton standing crop magnitudes were largely independent of long term acclimation temperatures.


pgs. 259-336


hydrology, ecosystems, river discharge, inflow, estuaries, biological production, plankton, primary production