Nutrient controls on ecosystem dynamics: the Chesapeake mesohaline community

Abstract

Ecological researchers have long borrowed concepts from the theory of chemical kinetics to describe nutrient dynamics in ecosystems. Contemporary ecology, however, is in the process of creating its own suite of ideas to quantify how whole ecosystems develop. In particular, the theory of ecosystem ascendency can be applied to data on the simultaneous flows of various chemical constituents to determine which element is limiting to each species via which individual input. That is, Liebig's law of the minimum appears a corollary to the broader description of whole-system development. Application of the method to networks of carbon, nitrogen and phosphorous flowing through the 36 major compartments of the Chesapeake Bay ecosystem reveals that, although nitrogen limits the production by most of the planktonic and benthic compartments, the nekton appear to be using phosphorus in limiting proportions. If one links together the ecosystem components via the controlling flows into each node, a new and sometimes dramatic picture of nutrient kinetics emerges. Not surprisingly, during the summer the root nutrient control on the system appears to be the recycle of nitrogen between particulate organic materials in the sediments and their attached bacteria. No coherent pattern of control is evident during the autumn turnover, whereas during winter and spring the ultimate control appears to be exerted by a feedback in the `microbial loop' that involves both N and P.