The Lake Washington PCB/PBDE Study: Development and testing of a PCB fate model

In 2010, King County was awarded a Puget Sound Action Agenda: Technical Investigations and Implementation Assistance Grant by the U.S. EPA to estimate loading of PCBs and PBDEs to Lake Washington, Lake Union and Puget Sound; and model potential reduction in Lake Washington fish tissue concentrations associated with select PCB loading reduction scenarios. A fate model was developed based on a simple two compartment (lake water and active sediment layer) model used to evaluate PCB fate in Lake Ontario and San Francisco Bay. An estimate of total PCB loading to Lake Washington based on field data collected as part of this study and model input values based on data specific to Lake Washington (when available) were used to test the model against observed water and sediment concentrations. Model sensitivity and uncertainty analyses were also conducted to identify critical model parameters and better understand the range in uncertainty in predicted water and sediment total PCB concentrations. The fate model was coupled to a food web bioaccumulation model, which is the subject of another conference presentation. More information, including the PCB fate and bioaccumulation modeling report can be found on the project website: http://www.kingcounty.gov/environment/watersheds/cedar-river-lake-wa/pcb-pbde-loadings.asp

The Lake Washington PCB/PBDE Study: Estimates of loading from major pathways

In 2010, King County was awarded a Puget Sound Action Agenda: Technical Investigations and Implementation Assistance Grant by the U.S. EPA to estimate loading of PCBs and PBDEs to Lake Washington, Lake Union and Puget Sound; and model potential reduction in Lake Washington fish tissue concentrations associated with select PCB loading reduction scenarios. A field study was designed and implemented from 2011 to 2012 to measure PCB and PBDE concentrations in key contaminant loading pathways to Lakes Washington and Union (i.e., rivers, streams, stormwater, CSOs, highway bridges and atmospheric deposition) and measure the concentrations in the export pathway leaving the lake system through the Ship Canal locks to Puget Sound. By combining the contaminant concentration data with long term flow estimates for these pathways, mass loading estimates to Lakes Washington and Union and subsequent export to Puget Sound for total PCBs and total PBDEs were developed. The approach to estimating pathway loads and loading estimates for each major pathway will be presented. More information, including the PCB/PBDE loadings report can be found on the project website: http://www.kingcounty.gov/environment/watersheds/cedar-river-lake-wa/pcb-pbde-loadings.asp

Assessing biological condition in small streams of the Puget Sound lowlands through collaborative regional monitoring

In 2015, the condition of Puget Sound Lowland streams was evaluated by collecting data for stream invertebrates, algae, water and sediment quality, and instream and riparian habitat. The study was designed and implemented as part of the Stormwater Action Monitoring program, a collaborative, regional stormwater monitoring program funded by more than 90 Western Washington cities and counties, the ports of Seattle and Tacoma, and the Washington State Department of Transportation. The goal of this long term program is to inform stakeholders on the status and trends of small streams within the Puget Lowlands and to track whether stream condition improves as a result of stormwater management practices in the region. A comparable number of sites were randomly selected inside and outside the Urban Growth Area (UGA). Benthic invertebrate taxa were used to calculate the benthic multi-metric index (B-IBI) and three stressor index scores for each of the 104 sites. All sites showed that sites within UGAs had poorer invertebrate condition compared to sites outside the UGA. Similar patterns were shown for algae, with the Trophic Diatom Index (TDI) indicating elevated nutrients inside the UGA compared to outside the UGA. We used boosted regression trees and a relative risk/attributable risk analysis to determine the most important human and natural factors influencing biological condition in the region. For the B-IBI, the most important factors influencing scores were December precipitation, watershed percent urban development, percent of watershed and riparian canopy cover, and stream substrate. For the TDI, the most important factors influencing condition were mean summer total phosphorus and nitrogen concentrations and watershed percent urban development. The intent is to use this status year of data to refine the sample design, and begin trend monitoring in the coming years with the goal to determine if streams are getting better or worse over time

The Lake Washington PCB/PBDE Study: Reductions Required and Recommendations

In 2010, King County was awarded a grant by the U.S. Environmental Protection Agency (EPA) to estimate total polychlorinated biphenyl (tPCB) and total polybrominated diphenylether (tPBDE) loadings to Lake Washington and from the Lake and Ship Canal to Puget Sound in Seattle Washington. The field study component of the project analyzed 146 samples for PCBs and PBDEs from 8 different matrices: (1) ambient Lake Washington water, (2) ambient Ship Canal waters, (3) three streams during both base flow and storm conditions, (4) the Cedar and Sammamish Rivers, (5) three combined sewer overflow (CSO) discharges, (6) six stormwater discharges, (7) combined wet and dry atmospheric deposition, and (8) one highway bridge discharge. Loadings estimates were developed for local drainages, major rivers, stormwater, CSOs, highways runoff and bulk deposition. Fate and bioaccumulation models were then used to describe the partitioning of the total PCB load between lake water, sediment, and biota. These models predicted a linear relationship between loadings and tissue concentrations. Coupling the loading, fate and bioaccumulation models predicts that an 85% loadings reduction is required to reduce tissue concentrations sufficiently to remove the existing WADOH consumption advisory. To achieve reductions of this magnitude, a suite of new or emerging treatment technologies in addition to aggressive source removal efforts to reduce the urban dome of PCBs in the region are going to be required in the Lake Washington watershed

The extent and variability of storm-induced temperature changes in lakes measured with long-term and high-frequency data

The intensity and frequency of storms are projected to increase in many regions of the world because of climate change. Storms can alter environmental conditions in many ecosystems. In lakes and reservoirs, storms can reduce epilimnetic temperatures from wind-induced mixing with colder hypolimnetic waters, direct precipitation to the lake's surface, and watershed runoff. We analyzed 18 long-term and high-frequency lake datasets from 11 countries to assess the magnitude of wind- vs. rainstorm-induced changes in epilimnetic temperature. We found small day-to-day epilimnetic temperature decreases in response to strong wind and heavy rain during stratified conditions. Day-to-day epilimnetic temperature decreased, on average, by 0.28 degrees C during the strongest windstorms (storm mean daily wind speed among lakes: 6.7 +/- 2.7 m s(-1), 1 SD) and by 0.15 degrees C after the heaviest rainstorms (storm mean daily rainfall: 21.3 +/- 9.0 mm). The largest decreases in epilimnetic temperature were observed >= 2 d after sustained strong wind or heavy rain (top 5(th) percentile of wind and rain events for each lake) in shallow and medium-depth lakes. The smallest decreases occurred in deep lakes. Epilimnetic temperature change from windstorms, but not rainstorms, was negatively correlated with maximum lake depth. However, even the largest storm-induced mean epilimnetic temperature decreases were typicallyPeer reviewe

Diel surface temperature range scales with lake size

Ecological and biogeochemical processes in lakes are strongly dependent upon water temperature. Long-term surface warming of many lakes is unequivocal, but little is known about the comparative magnitude of temperature variation at Diel timescales, due to a lack of appropriately resolved data. Here we quantify the pattern and magnitude of Diel temperature variability of surface waters using high-frequency data from 100 lakes. We show that the near-surface Diel temperature range can be substantial in summer relative to long-term change and, for lakes smaller than 3 km2, increases sharply and predictably with decreasing lake area. Most small lakes included in this study experience average summer Diel ranges in their near-surface temperatures of between 4 and 7°C. Large Diel temperature fluctuations in the majority of lakes undoubtedly influence their structure, function and role in biogeochemical cycles, but the full implications remain largely unexplored

The state of the Martian climate

60°N was +2.0°C, relative to the 1981–2010 average value (Fig. 5.1). This marks a new high for the record. The average annual surface air temperature (SAT) anomaly for 2016 for land stations north of starting in 1900, and is a significant increase over the previous highest value of +1.2°C, which was observed in 2007, 2011, and 2015. Average global annual temperatures also showed record values in 2015 and 2016. Currently, the Arctic is warming at more than twice the rate of lower latitudes

Diel surface temperature range scales with lake size

Ecological and biogeochemical processes in lakes are strongly dependent upon water temperature. Long-term surface warming of many lakes is unequivocal, but little is known about the comparative magnitude of temperature variation at diel timescales, due to a lack of appropriately resolved data. Here we quantify the pattern and magnitude of diel temperature variability of surface waters using high-frequency data from 100 lakes. We show that the near-surface diel temperature range can be substantial in summer relative to long-term change and, for lakes smaller than 3 km2, increases sharply and predictably with decreasing lake area. Most small lakes included in this study experience average summer diel ranges in their near-surface temperatures of between 4 and 7°C. Large diel temperature fluctuations in the majority of lakes undoubtedly influence their structure, function and role in biogeochemical cycles, but the full implications remain largely unexplored

A framework for ensemble modelling of climate change impacts on lakes worldwide : the ISIMIP Lake Sector

Empirical evidence demonstrates that lakes and reservoirs are warming across the globe. Consequently, there is an increased need to project future changes in lake thermal structure and resulting changes in lake biogeochemistry in order to plan for the likely impacts. Previous studies of the impacts of climate change on lakes have often relied on a single model forced with limited scenario-driven projections of future climate for a relatively small number of lakes. As a result, our understanding of the effects of climate change on lakes is fragmentary, based on scattered studies using different data sources and modelling protocols, and mainly focused on individual lakes or lake regions. This has precluded identification of the main impacts of climate change on lakes at global and regional scales and has likely contributed to the lack of lake water quality considerations in policy-relevant documents, such as the Assessment Reports of the Intergovernmental Panel on Climate Change (IPCC). Here, we describe a simulation protocol developed by the Lake Sector of the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP) for simulating climate change impacts on lakes using an ensemble of lake models and climate change scenarios for ISIMIP phases 2 and 3. The protocol prescribes lake simulations driven by climate forcing from gridded observations and different Earth system models under various representative greenhouse gas concentration pathways (RCPs), all consistently bias-corrected on a 0.5 degrees x 0.5 degrees global grid. In ISIMIP phase 2, 11 lake models were forced with these data to project the thermal structure of 62 well-studied lakes where data were available for calibration under historical conditions, and using uncalibrated models for 17 500 lakes defined for all global grid cells containing lakes. In ISIMIP phase 3, this approach was expanded to consider more lakes, more models, and more processes. The ISIMIP Lake Sector is the largest international effort to project future water temperature, thermal structure, and ice phenology of lakes at local and global scales and paves the way for future simulations of the impacts of climate change on water quality and biogeochemistry in lakes.Peer reviewe