We describe continental-scale increases in lake and stream total phosphorus (TP) concentrations, identified through periodic probability surveys of thousands of water bodies in the conterminous U.S. The increases, observed over the period 2000-2014 were most notable in sites in relatively undisturbed catchments and where TP was initially low (e.g., less than 10 μg L(-1)). Nationally, the percentage of stream length in the U.S. with TP ≤ 10 μg L(-1) decreased from 24.5 to 10.4 to 1.6% from 2004 to 2009 to 2014; the percentage of lakes with TP ≤ 10 μg L(-1) decreased from 24.9 to 6.7% between 2007 and 2012. Increasing TP concentrations appear to be ubiquitous, but their presence in undeveloped catchments suggests that they cannot be entirely attributed to either point or common non-point sources of TP.

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Alternative futures analysis can inform community decisions regarding land and water use. We conducted an alternative futures analysis in the Willamette River Basin in western Oregon. Based on detailed input from local stakeholders, three alternative future landscapes for the year 2050 were created and compared to present‐day (circa 1990) and historical (pre‐EuroAmerican settlement) landscapes. We evaluated the likely effects of these landscape changes on four endpoints: water availability, Willamette River, stream condition, and terrestrial wildlife. All three futures assume a doubling of the 1990 human population by 2050. The Plan Trend 2050 scenario assumes current policies and trends continue. Because Oregon has several conservation‐oriented policies in place, landscape changes and projected environmental effects associated with this scenario were surprisingly small (most ≤10% change relative to 1990). The scenario did, however, engender a debate among stakeholders about the reasonableness of assuming that existing policies would be implemented exactly as written if no further policy actions were taken. The Development 2050 scenario reflects a loosening of current policies, more market‐oriented approach, as proposed by some stakeholders. Estimated effects of this scenario include loss of 24% of prime farmland; 39% more wildlife species would lose habitat than gain habitat relative to the 1990 landscape. Projected effects on aquatic biota were less severe, primarily because many of the land use changes involved conversion of agricultural lands into urban or rural development, both of which adversely impact streams. Finally, Conservation 2050 assumes that ecosystem protection and restoration are given higher priority, although still within the bounds of what stakeholders considered plausible. In response, most ecological indicators (both terrestrial and aquatic) recovered 20–70% of the losses sustained since EuroAmerican settlement. The one exception is water availability. Water consumed for out‐of‐stream uses increased under all three future scenarios (by 40–60%), with accompanying decreases in stream flow. Although the conservation measures incorporated into Conservation 2050 moderated the increase in consumption, they were not sufficient to reverse the trend. Results from these analyses have been actively discussed by stakeholder groups charged with developing a vision for the basin's future and a basin‐wide restoration strategy.

As part of the Episodic Response Project (ERP), we intensively monitored discharge and stream chemistry of 13 streams located in the Northern Appalachian region of Pennsylvania and in the Catskill and Adirondack Mountains of New York from fall 1988 to spring 1990. The ERP clearly documented the occurrence of acidic episodes with minimum episodic pH ≤ 5 and inorganic monomeric Al (Alim) concentrations > 150 μg/L in at least two study streams in each region. Several streams consistently experienced episodes with maximum Alim concentrations >350 μg/L. Acid neutralizing capacity (ANC) depressions resulted from complex interactions of multiple ions. Base cation decreases often made the most important contributions to ANC depressions during episodes. Organic acid pulses were also important contributors to ANC depressions in the Adirondack streams, and to a lesser extent, in the Catskill and Pennsylvania streams. Nitrate concentrations were low in the Pennsylvania streams, whereas the Catskill and Adirondack study streams had high NO3‐ concentrations and large episodic pulses (≤ 54 μ eq/L). Most of the Pennsylvania study streams also frequently experienced episodic pulses of SO42‐ (≤ 78 μ eq/L), whereas the Adirondack and Catskill streams did not. High baseline concentrations of SO42‐ (all three study areas) and NO3‐ (Adirondacks and Catskills) reduced episodic minimum ANC, even when these ions did not change during episodes. The ion changes that controlled the most severe episodes (lowest minimum episodic ANC) differed from the ion changes most important to smaller, more frequent episodes. Pulses of NO3‐ (Catskills and Adirondacks), SO42‐ (Pennsylvania), or organic acids became more important during major episodes. Overall, the behavior of streamwater SO42‐ and NO3‐ is an indicator that acidic deposition has contributed to the severity of episodes in the study streams.

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