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Background
Background
Rivers and Cities
Rivers and Cities
In human population centers, rivers serve as a source of water for drinking, industry, and irrigation, and a place for transportation, recreation, and waste disposal. A critical challenge for scientists is characterizing past and current influences of human activities on river ecosystems and then predicting and mitigating future human impacts to maintain the beneficial ecological functions of rivers.
While general hydrological and ecological frameworks have been developed for stream systems, the effects of human activities across space (e.g., headwaters to large rivers, old vs new development) and time (e.g., seasons, with precipitation) are not adequately represented by existing ecosystem models. We seek to understand how human activities affect the spatial and temporal scales of ecological processes differently in different cities.
Examples of human impacts on ecological processes on rivers:
Examples of human impacts on ecological processes on rivers:
Wastewater infrastructure. Untreated wastewater is introduced to streams and rivers through leaky septic systems and sewer lines, direct dumping, and combined sewer overflows (CSOs). Bacteria in wastewater contaminates waterways and excess nutrients lead to algal blooms, hypoxia, and changes in aquatic biota.
Riparian vegetation. In naturally vegetated watersheds, the addition or removal of plants adjacent to streams influences the water temperature, light availability, and nutrient availability for organisms living in streams.
Culverts and burial. Streams in cities are often routed through culverts or covered for long stretches, changing the light and temperature conditions of the water and influencing rates of metabolism by stream organisms.
Channelization. Lining stream channels with impervious materials (stone or cement) alters the hydrology, leading to more rapid flows. Additionally, channelized streams are separated from plant roots and sediments on the stream bed and banks, preventing geochemical cycling of nutrients and filtering of contaminants.
Stormwater runoff. Impervious land cover, such as streets and parking lots, rapidly route unfiltered stormwater into streams, resulting in flashy flows and bringing along oils, road salts, fertilizers, and other pollutants.
River Fragmentation. Dams, impoundments, and irrigation diversions, in addition to some river and stream crossings (bridges and culverts) fragment river systems and prevent the movement of biota along the length of the river. These structures also alter flow and change the timing and magnitude of nutrients and sediments moving through urban river systems, which are critical to the habitats and life cycles of riverine organisms.
Carbon Cycling in Urban Rivers
Carbon Cycling in Urban Rivers
While the global carbon cycle has received much attention, the magnitude and characteristics of carbon fluxes in rivers, particularly those impacted by human activities, are key factors in assessments and models of global sources and sinks of carbon. Human activities influence the timing and scale of carbon cycling within watersheds, introduce novel sources of carbon, and mobilize previously inactive carbon sources.
DOC represents the largest flux of carbon in streams and includes organic compounds of varying composition that are smaller than about 0.2 microns. DOC may enter river systems through atmospheric deposition and recharge from groundwater that has passed through organic rich soils or wetlands; DOC may also be produced directly in the river by organisms such as algae or macrophytes and the degradation of particulate organic matter such as leaf litter. Additional human sources include sewage and organic materials in stormwater runoff.
Why Carbon Matters
Why Carbon Matters
In addition to better constraining the riverine sources and sinks within the global carbon cycle, studying DOC is important to all stream ecological functions and water quality.
Examples of the roles of DOC in stream ecology:
Examples of the roles of DOC in stream ecology:
Source of energy and carbon for heterotrophic organisms. DOC is a primary energy source in aquatic food webs. The cycling of nutrients (nitrogen and phosphorous) is tied to these carbon metabolizing processes. For example, nitrate concentration is tied to denitrification rates, which are influenced by DOC availability.
Interaction with light and UV radiation. DOC absorbs UV radiation and visible light, so the concentration of DOC influences light availability for photosynthetic organisms.
Contaminant transport and water quality. Dissolved organic material serves as binding sites for potentially harmful organic compounds and trace metals, influencing their transport and release.
Project Goals
Project Goals
The primary objective of the Carbon in Urban River Biogeochemistry Project (CURB) is to assess how human controls (e.g., wastewater infrastructure, housing density) and biophysical controls (e.g., discharge, precipitation) on riverine DOC concentrations, characteristics, and bioavailability (how readily it can be used by organisms) vary across geographies and urban context.
Rivers and the landscapes through which they flow vary widely in both human factors (e.g., wastewater infrastructure, housing density, impervious surfaces) and biophysical factors (e.g., discharge, precipitation, temperature, canopy cover). A key goal of CURB is analyzing how these factors and their interactions influence DOC (and therefore stream function) among cities. Five cities across the US will serve as study areas representing distinct urban typologies.
Studying the human influence on carbon in rivers will improve forecasting and the design of mitigation strategies for carbon release from streams. Additionally, due to the central role of organic carbon within aquatic ecosystems, this research will lead to better understanding of stream ecosystem structure and function, informing policies and strategies for the restoration of urban streams and rivers.
Field and Laboratory Research
Field and Laboratory Research
Water samples collected in urban rivers will be analyzed for DOC concentration, bioavailability (through degradation and enzyme activity analyses), and fluorescence (which provides insight into the type and source of DOC). Additional measurements of stream discharge, temperature, pH, conductivity, and dissolved oxygen (DO) will help contextualize spatial and temporal trends in DOC. Taken together, these data will lead to better understanding of human and biophysical controls on DOC across urban rivers and provide important information for carbon budgets and river management. The project consists of two major field components:
Synoptic Sampling
Synoptic Sampling
In each city, one hundred stream sites will be selected to reflect differences in land use, impervious cover, riparian vegetation, and stream size. Water samples will be collected at each of these sites during 4 synoptic sampling events over the course of one year to examine seasonal difference in carbon chemistry.
Installed Sensors
Installed Sensors
At three of the sites, sensors will be temporarily installed to measure dissolved organic matter, temperature, pH, conductivity, turbidity, and optical brighteners (an indicator of wastewater contamination). Measurements will be logged every 15 minutes for one year, and data will be correlated with discharge measurements from nearby USGS gages to analyze how stream water characteristics change over time in urban watersheds with different properties.
More information:
More information:
This work is being carried out collaboratively by researchers at the institutions listed below.
Contact information for researchers in each study area is available on the People page.
This research is funded by the National Science Foundation, Award Abstract 2015616: “Scales and drivers of variability in dissolved organic carbon across diverse urban watersheds”
CURB_ProjectOverview_3-25-22.pdfPlease click the pop-out button on the document for a PDF version of the project overview.
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