the [inter]relations

"Three hundred trout are needed to support one man for a year. The trout, in turn, must consume 90,000 frogs, that must consume 27 million grasshoppers that live off of 1,000 tons of grass."
-- G. Tyler Miller, Jr., American Chemist (1971)

This is a reoccurring quote when measuring an ecosystem's health, which refers to the transference of nutrients, or energy, through trophic relations. The bottom line is that man, or any widespread carnivorous mammal, although not directly dependent on sunlight for energy, can trace any food source to a primary source,or the primary production, in all cases to the sun.
At a simplified glance, a plant requires sunlight, carbon dioxide, water, and nutrients, and through photosynthesis produces reduced carbon compounds and oxygen.(1) This simply stated process, in theory, allows the energy-devouring plants to develop further, thus increasing the potential for more plant life from their prospective offspring, and thus increasing an environment's relative 'biomass'.
The measure of the environment's primary production serves as an accurate way of measuring the complexity of a region because all other forms of life will be dependent on plant life in both direct and indirect ways.
An abundance of plant life serves for an abundance of nutrient availability for all other forms of life, through an interweaving web of digestive connections; eg. through herbivore species, followed through to carnivorous species. The increase of plant biomass within the environment can even satiate the region's detrivore populations with the addition of decomposing materials(2).
This dependent relation is of primary production is at the heart of any healthy river system. It can be well assumed that urbanization in the northern east coast has altered these primary production levels among the Delaware River. The introduction of toxins to the water can disrupt natural processes. Even waste pollution, as simple as a discarded paper cup, can out-compete biotic species in oxygen through its decomposition. That single cup may serve as a fatal final-blow, if it drifts upon an ecosystem that already faces a continuing battle with dissolved oxygen levels-a struggle that originated with a reduction in of primary production.
One of the key factors in primary production among aquatic ecosystems is nutrient availability, and human disturbances continue to have an increasing effect on the natural nutrient recycling processes by contributing foreign chemicals and toxins. The environmental symbiosis between terrestrial runoff and aquatic health is highly sensitive. Human development disrupts natural occurrences that have spent eras in accordance of geological perfection. The sensitivity of such environmental symbiosis was observed in a case study in Ontario, Canada, where the conversion of forested land for agricultural use increased phosphorus runoff by 4x, and Urban conditions contribute 9x more phosphorus than forest land with vegetative buffered zones(2, 450-451).

As observed from the chart above, although the Delaware River is said to be of the healthiest in the nation, it's primary production rate is lower in comparison to other U.S. rivers that are not as severely affected by urban patterns.

River biota, like all life, seem to operate in these intricate bio/geo/chemical associations with all other species within their shared region. Influencing one missing link in a food web may affect the status of many species.
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1.) http://www.physicalgeography.net
2.) Molles, Manuel C. Ecology: Concepts and Applications, McGrawHill 2008