Wastewater continues to be a significant input to the Hudson River. In the past, the effects of large amounts of wastewater have been well-documented, but the consequences of more dilute wastewater concentrations on river functioning have not been considered. Therefore, we focused on examining how varying concentrations of wastewater affects the bacteria and phytoplankton communities in the Hudson River. To do this, Hudson River water samples were amended with amounts of wastewater spanning the relative inputs observed in the system. To evaluate the bacterial response, we measured oxygen consumption, the dissolved organic carbon (DOC) concentration, nitrate and phosphorus concentrations, and the optical properties of dissolved organic matter (DOM) over a two week span. The DOM optical properties were quantified using the UV-visible curve spectral slopes, absorption at 300 nm, and a PARAFAC analysis of fluorescent DOM in all samples. In addition, the phytoplankton response was measured as the accumulation of chlorophyll a in the samples. Using all of the data, a two-way ANOVA (where a p-value of less than 0.05 was considered significant) was performed to help understand the significant differences in all of the parameters measured with respect to time and wastewater concentration.
Results/Conclusions
The addition of wastewater significantly increased the concentrations of nitrate, phosphorus, and DOC. The 50% wastewater sample showed 50% higher nitrate and 70% higher phosphorus concentrations compared to the 0% wastewater sample. The 50% wastewater and 100% wastewater samples showing approximately 6% and 4% increase in DOC, respectively, relative to the 0% wastewater sample. The biological oxygen demand, optical properties of DOM, and concentration of cholorphyll a did not significantly change with increasing wastewater concentrations. These results demonstrate that the wastewater did not stimulate bacterial oxygen consumption, did not alter the bioavailability of DOM, and did not stimulate phytoplankton growth. Therefore, the input of dilute concentrations of wastewater does add nutrients and DOC into the system, but does not significantly alter the functioning of the bacteria and phytoplankton communities. This could be due to multiple reasons. One being that wastewater treatment plants are efficiently treating wastewater. Another being that the Hudson River already receives a fair amount of wastewater so additional wastewater does not have as much of an impact. Either way, the treated wastewater may contain other things like pharmaceuticals, household chemicals, and indicator microbes that could be affecting other parts of the system that we did not examine.