Exploring spatial and temporal symptoms of the freshwater salinization syndrome in a rural to urban watershed.

The freshwater salinization syndrome (FSS), a concomitant watershed-scale increase in salinity, alkalinity, and major-cation and trace-metal concentrations, over recent decades, has been described for major rivers draining extensive urban areas, yet few studies have evaluated temporal and spatial FSS variations, or causal factors, at the subwatershed scale in mixed-use landscapes. This study examines the potential influence of land-use practices and wastewater treatment plant (WWTP) effluent on the export of major ions and trace metals from the mixed-use East Branch Brandywine Creek watershed in southeastern Pennsylvania, during the 2019 water year. Separate analysis of baseflow and stormflow subsets revealed similar correlations among land-use characteristics and streamwater chemistry. Positive associations between percent impervious surface cover, which ranged from 1.26 % to 21.9 % for the 13 sites sampled, and concentrations of Ca2+, Mg2+, Na+, and Cl- are consistent with road-salt driven reverse cation exchange and weathering of the built environment. The relative volume of upstream WWTP was correlated with Cu and Zn, which may be derived in part from corroded water-conveyance infrastructure; chloride to sulfate mass ratios (CSMR) ranged from ~6.3 to ~7.7× the 0.5 threshold indicating serious corrosivity potential. Observed exceedances of U.S. Environmental Protection Agency Na+ and Cl- drinking water and aquatic life criteria occurred in winter months. Finally, correlations between percent cultivated cropland and As and Pb concentrations may be explained by the persistence of agricultural pesticides that had been used historically. Study results contribute to the understanding of FSS solute origin, fate, and transport in mixed-use watersheds, particularly those in road salt-affected regions. Study results also emphasize the complexity of trace-metal source attribution and explore the potential for FSS solutes to affect human health, aquatic life, and infrastructure.

Metal accumulation in salt marsh soils along the East Coast of the United States.

Coastal salt marshes are depositional environments that can accumulate pollutants introduced to the environment from human activities. Metals are a contaminant of concern in coastal environments due to their longevity and toxicity. We assessed metal concentrations and accumulation rates in nine salt marsh sites along the U.S. East Coast from Maine to Georgia. Following a metal mobility assay in organic-rich and mineral dominated salt marsh soils under aerobic/anaerobic and freshwater/saltwater conditions, we focused on profiles of chromium, nickel, copper, zinc, cadmium, lead, and uranium in two soil cores from each of the nine marshes that had previously been dated using lead-210 radioisotope techniques. We examined how land cover and the spatial distribution of land cover, marsh vertical accretion, and other watershed characteristics correlated with metal concentrations and depth/time-integrated accumulation of metals. We found statistically significant differences in metal concentrations and/or inventories between sites, with accumulation of metals positively correlated with both developed land cover in the watershed and rates of vertical accretion in the tidal marsh. The accumulation of chromium, cadmium, and lead were significantly correlated with developed land cover while the accumulation of chromium, nickel, copper, zinc, and lead were correlated with factors that determine sediment delivery from the landscape (e.g., riverine suspended sediment, soil erodibility in the watershed, and agricultural land cover skewed towards the coast) and measured wetland accretion rates. We observed declines in the concentration of many metals since 1925 at sites along the U.S. East Coast, indicating pollution mitigation strategies have succeeded in reducing metal pollution and delivery to the coastal zone. However, increasing rates of salt marsh vertical accretion over recent decades largely offset reductions in metal concentrations, resulting in rates of metal accumulation in coastal salt marsh soils that have not changed or, in some instances, increased over time.

Long-term impacts of impervious surface cover change and roadway deicing agent application on chloride concentrations in exurban and suburban watersheds.

Roadway deicing agents, including rock salt and brine containing NaCl, have had a profound impact on the water quality and aquatic health of rivers and streams in urbanized areas with temperate climates. Yet, few studies evaluate impacts to watersheds characterized by relatively low impervious surface cover (ISC; < 15 %). Here, we use long-term (1997-2019), monthly streamwater quality data combined with daily streamflow for six exurban and suburban watersheds in southeastern Pennsylvania to examine the relations among chloride (Cl-) concentrations and ISC. Both flow-normalized Cl- concentrations and ISC increased over time in each of the six watersheds, consistent with changes in watershed management (e.g., ISC, road salt application, etc.). The watersheds that experienced the greatest changes in percent ISC (e.g., agriculture replaced by residential and commercial development) experienced the greatest changes in flow-normalized Cl- concentrations. We also utilized a comprehensive mass-balance model (2011-2018) that indicated Cl- inputs exceeded the outputs for the study watersheds. Road salt applied to state roads, non-state roads, and other impervious surfaces accounted for the majority of Cl- inputs to the six watersheds. Furthermore, increasing Cl- concentrations during baseflow conditions confirm impacts to shallow groundwater. Although flow-normalized Cl- concentrations are below the U.S. Environmental Protection Agency's chronic threshold value for impacts to aquatic organisms, year-round exceedances may result before the end of this century based on current trends. Though reduced Cl- loading to streams may be achieved by limiting the expansion of impervious surfaces in exurban and suburban watersheds, changes in baseflow concentrations are likely to be gradual because of the accumulated Cl- in groundwater.

Bioaccumulation of trace metals in two oyster species from southwest Puerto Rico.

As coastal ecosystems are impacted by land use change and anthropogenic activities, oysters can be an important tool for monitoring local water quality. We collected oysters (Crassostrea rhizophorae and Isognomon alatus) from coastal sites near Guánica and La Parguera in southwest Puerto Rico and analyzed their tissue for concentrations of Ag, As, Cd, Co, Cr, Cu, Ni, Pb, V, and Zn. All trace metals were found in both species, with high bioaccumulation factors for Ag, Cd, and Zn in both species and Cr in C. rhizophorae. Some trace metals are likely associated with anthropogenic sources, including paints and vehicles (Cu and Zn), oil (Ni and V), and wood preservatives (As). Cr in oysters near Guánica is most likely associated with sediment from erosion in the watershed. Both species could be used to monitor changes in trace metal concentrations and the influence of future watershed management strategies in the region.

Impacts of Road Deicing Application on Sodium and Chloride Concentrations in Philadelphia Region Drinking Water.

Historical application of roadway deicing agents (e.g., road salt and brines) has led to an increase in sodium and chloride concentrations in surface water over time. Numerous studies have explored the impacts of road salt on freshwater aquatic organisms such as amphibians and benthic macroinvertebrates; however, the public health risk associated with consuming drinking water with elevated sodium has been largely unexplored in the literature. Yet, sodium ingestion, primarily through diet, has been linked to adverse human health conditions, such as hypertension. This study documents weekly sodium and chloride concentrations in municipal tap water from three municipalities within the Philadelphia metropolitan area during winter 2018-2019 (November through March). A late winter peak in sodium and chloride concentrations was observed for all three municipalities immediately following successive snow events coupled with daily high temperatures above 0°C. Among municipalities, mean and peak sodium and chloride concentrations were associated with relatively higher development in upstream areas. Observed sodium concentrations ranged from 1 to 6.4x the USEPA recommended guideline of 20 mg/L for individuals restricted to a total sodium intake of 500 mg/day. Additionally, the contribution of sodium ingestion from water consumption to the recommended daily sodium intake limits for adults ranged from 3.5% to 18.8% for non-restricted and 4.2%-33.3% for "low salt" (i.e., <1,500 mg/day) diets, respectively. The study results coupled with a records review for 40 U.S. municipalities in snow affected regions indicate the need for real-time communication between water utilities and the general public regarding sodium exposure risk during winter months.

Physical controls and ENSO event influence on weathering in the Panama Canal Watershed.

Recent empirical studies have documented the importance of tropical mountainous rivers on global silicate weathering and suspended sediment transport. Such field studies are typically based on limited temporal data, leaving uncertainty in the strength of observed relationships with controlling parameters over the long term. A deficiency of long-term data also prevents determination of the impact that multi-year or decadal climate patterns, such as the El Niño Southern Oscillation (ENSO), might have on weathering fluxes. Here we analyze an 18-year hydrochemical dataset for eight sub-basins of the Panama Canal Watershed of high-temporal frequency collected between 1998 and 2015 to address these knowledge gaps. We identified a strongly positive covariance of both cation (Ca2+, Mg2+, K+, Na+) and suspended sediment yields with precipitation and extent of forest cover, whereas we observed negative relationships with temperature and mosaic landcover. We also confirmed a statistical relationship between seasonality, ENSO, and river discharge, with significantly higher values occurring during La Niña events. These findings emphasize the importance that long-term datasets have on identifying short-term influences on chemical and physical weathering rates, especially, in ENSO-influenced regions.

Triclosan export from low-volume sources in an urban to rural watershed.

Triclosan (TCS), an emerging contaminant linked to antimicrobial resistance, has been the focus of many surface water studies to date. However, these initial studies have predominantly used sampling locations downstream of large volume (i.e., >0.5 million gallons per day) wastewater treatment plants (WWTPs). This approach overlooks potential inputs from their low volume counterparts as well as non-point sources, such as sewage network leaks, biosolid application to agricultural fields and leach fields associated with septic systems. Here we examine the range of concentrations, overall loading, and potential controls on TCS delivery to the East Branch of the Brandywine Creek (EBBC), a rural to suburban watershed located in southeastern Pennsylvania. TCS measurements were collected from 13 locations in the EBBC during baseflow conditions and immediately following a storm event. A regulatory database review identified WWTP density an order of magnitude greater than the national average, thereby confirming their pervasiveness in rural to urban systems. Detectable concentrations of TCS in the EBBC ranged from 0.2 to 0.6 ng/L during baseflow conditions and 0.5 to over 1000 ng/L following a storm event. The lack of a statistical relationship between TCS concentrations and yields with the number of upstream WWTPs and/or volume of treated effluent during both sampling periods confirm the importance of individual WWTP practices and the volume of the receiving water body, while a positive statistically-significant relationship between TCS concentrations and upstream developed open space following the storm event was likely influenced by runoff of spray-applied treated wastewater and/or sewage network leaks. Furthermore, the presence of detectable concentrations of TCS in sub-watersheds with no WWTP systems implies field applied biosolids or treated wastewater, as well as septic tank related leach fields are all viable sources of TCS. These findings suggest we must greatly expand our consideration of sources for emerging contaminants in waterways.