Water quality patterns in a river-lake system from multiple drivers (Three Rivers, New York State)

Abstract

Robust spatial patterns of common water quality metrics are resolved for the downstream 90 km of the Three Rivers system of New York State (USA), extending to its entry into Lake Ontario, to assess water quality status and document signatures from an array of stressors and drivers. The strong longitudinal and vertical signatures documented are based on eight high spatial resolution (vertical profiles at 50 sites) summer surveys of temperature, specific conductance, turbidity, fluorometric chlorophyll a, dissolved oxygen, and nitrate. The water quality of three upstream boundary waters is also documented based on continuous concurrent measurements from robotic monitoring platforms. The spatial signatures along the river system are demonstrated to be driven by: (1) the major differences in the water quality of boundary water inputs, (2) physical modification of the river system that reduces turbulence and promotes vertical stratification, (3) the configuration of three lakes within this system, (4) inputs from waste water treatment plants, and (5) the zebra mussel invasion. The oxygen resources of this river system are shown to be degraded; e.g., water quality standards for dissolved oxygen were not met for 31 km of river length in one survey. The character and causes of the dissolved oxygen problems represent severe challenges for rehabilitation, which may require interventions to recover turbulence. A robotic monitoring program is recommended, with unit deployment locations guided by the surveys of this study, to stay apprised of water quality status and support water quality modeling initiatives. Development of a water quality model is recommended to guide management deliberations for recovery of oxygen resources, which will require a robust hydrodynamic transport framework to represent the complexities of this system.