We examined the geographic extent of petroleum hydrocarbon contamination in sediment, seawater, biota, and seafood during/after the BP/Deepwater Horizon Oil Spill (April 20-July 15, 2010; 28.736667°N, -88.386944°W). TPH, PAHs, and 12 compound classes were examined, particularly C1-benzo(a)anthracenes/chrysenes, C-2-/C-4-phenanthrenes/anthracenes, and C3-naphthalenes. Sediment TPH, PAHs, and all classes peaked near Pensacola, Florida, and Galveston, Texas. Seawater TPH peaked off Pensacola; all of the above classes peaked off the Mississippi River, Louisiana and Galveston. Biota TPH and PAHs peaked near the Mississippi River; C-3 napthalenes peaked near the spill site. Seafood TPH peaked near the spill site, with PAHs and all classes peaking near Pensacola. We recommend that oil concentrations continued to be monitored in these media well after the spill has ceased to assist in defining re-opening dates for fisheries; closures should be maintained until hydrocarbon levels are deemed within appropriate limits.

We conducted a resurvey of the O horizon in 2001 in watersheds previously sampled in 1984 under the Direct/Delayed Response Program (DDRP) to evaluate the effects of reductions in acidic deposition in the northeastern United States. In this 17‐yr interval, median base saturation in the Oa horizon decreased from 56.2% in 1984 to 33.0% in 2001. Effective cation exchange capacity (CECe), normalized to soil C concentration, showed no significant change between 1984 and 2001. The change in base saturation was the result of almost equivalent changes in C‐normalized exchangeable Ca (CaN) and exchangeable Al (AlN). The median CaN declined by more than 50%, from 23.5 to 10.6 cmolc kg−1 C, while median AlN more than doubled, from 8.8 to 21.3 cmolc kg−1 C. We observed the greatest change in soil acid–base properties in the montane regions of Central New England (CNE) and Maine, where base saturation decreased by more than 50% and median soil pH in 0.01 M CaCl2 (pHs) decreased from 3.19 to 2.97. Changes in median concentrations of other exchangeable cations were either statistically insignificant (MgN, KN) or very small (NaN). We observed no significant change in the median values of either total soil C content (%C) or total soil N content (%N) over the 17‐yr interval. The acidification of the Oa horizon between 1984 and 2001 occurred despite substantial reductions in atmospheric acidic deposition. Our results may help to explain the surprisingly slow rate of recovery of surface waters.

Atmospheric deposition of nitrogen (N) influences forest demographics and carbon (C) uptake through multiple mechanisms that vary among tree species. Prior studies have estimated the effects of atmospheric N deposition on temperate forests by leveraging forest inventory measurements across regional gradients in deposition. However, in the United States (U.S.), these previous studies were limited in the number of species and the spatial scale of analysis, and did not include sulfur (S) deposition as a potential covariate. Here, we present a comprehensive analysis of how tree growth and survival for 71 species vary with N and S deposition across the conterminous U.S. Our analysis of 1,423,455 trees from forest plots inventoried between 2000 and 2016 reveals that the growth and/or survival of the vast majority of species in the analysis (n = 66, or 93%) were significantly affected by atmospheric deposition. Species co-occurred across the conterminous U.S. that had decreasing and increasing relationships between growth (or survival) and N deposition, with just over half of species responding negatively in either growth or survival to increased N deposition somewhere in their range (42 out of 71). Averaged across species and conterminous U.S., however, we found that an increase in deposition above current rates of N deposition would coincide with a small net increase in tree growth (1.7% per Δ kg N ha-1 yr-1), and a small net decrease in tree survival (-0.22% per Δ kg N ha-1 yr-1), with substantial regional and among-species variation. Adding S as a predictor improved the overall model performance for 70% of the species in the analysis. Our findings have potential to help inform ecosystem management and air pollution policy across the conterminous U.S., and suggest that N and S deposition have likely altered forest demographics in the U.S.

Changes in lake water chemistry between 1984 and 2001 at 130 stratified random sites across the northeastern United States were studied to evaluate the population-level effects of decreases in acidic deposition. Surface-water SO4 2- concentrations decreased across the region at a median rate of −1.53 μequiv L-1 year-1. Calcium concentrations also decreased, with a median rate of −1.73 μequiv L-1 year-1. This decrease in Ca2+ retarded the recovery of surface water acid neutralizing capacity (Gran ANC), which increased at a median rate of 0.66 μequiv L-1 year-1. There were small increases in pH in all subregions except central New England and Maine, where the changes were not statistically significant. Median NO3 - trends were not significant except in the Adirondacks, where NO3 - concentrations increased at a rate of 0.53 μequiv L-1 year-1. A regionwide decrease in the concentration of total Al, especially in ponds with low ANC values (ANC < 25 μequiv L-1), was observed in the Adirondack subregion. These changes in Al were consistent with the general pattern of increasing pH and ANC. Despite the general pattern of chemical recovery, many ponds remain chronically acidic or are susceptible to episodic acidification. The continued chemical and biological recovery at sites in the northeastern United States will depend on further controls on S and N emissions.