Sources and transformation of carbon (C) were quantified using mass balance
and ecosystem metabolism data for the upper segments of the James, Pamunkey
and Mattaponi estuaries. The goal was to assess ...the role of external (river
inputs and tidal exchange) vs. internal (metabolism) drivers in influencing
the forms and fluxes of C. C forms and their response to river discharge
differed among the estuaries based on their physiographic setting. The
James, which receives the bulk of inputs from upland areas (Piedmont and
Mountain), exhibited a higher ratio of inorganic to organic C and larger
inputs of particulate organic C (POC). The Pamunkey and Mattaponi receive a
greater proportion of inputs from lowland (Coastal Plain) areas, which were
characterized by low dissolved inorganic C (DIC) and POC and elevated
dissolved organic C (DOC). I anticipated that transport processes would
dominate during colder months when discharge is elevated and metabolism is
low and that biological processes would predominate in summer, leading to
attenuation of C throughputs via degassing of CO2. Contrary to
expectations, the highest retention of organic C occurred during periods of high
throughput, as elevated discharge resulted in greater loading and retention
of POC. In summer, internal cycling of C via production and respiration was
large in comparison to external forcing despite the large riverine influence
in these upper-estuarine segments. The estuaries were found to be net
heterotrophic based on retention of organic C, export of DIC, low primary
production relative to respiration and a net flux of CO2 to the
atmosphere. In the James, greater contributions from phytoplankton
production resulted in a closer balance between production and respiration,
with autochthonous production exceeding allochthonous inputs. Combining the
mass balance and metabolism data with bioenergetics provided a basis for
estimating the proportion of C inputs utilized by the dominant metazoan. The
findings suggest that invasive catfish utilize 15 % of total organic C
inputs and up to 40 % of allochthonous inputs to the James.
Lake surveys conducted in 1987–88 and 2018–19 show changes in the chemical and optical properties of Adirondack lakes recovering from acidification. Among chronically acidified lakes (1980s pH < 5.5, ...ANC < 0 µeq L
−1
), increases in pH and reductions in monomeric Al were accompanied by significant increases in light attenuation, DOC, and CDOM. DOC-specific dissolved color (CDOM:DOC) doubled over the 30-year span, and is the likely factor accounting for loss of water clarity in Adirondack lakes during recovery from acidification. Monitoring data (1994–2002) from a subset of these lakes show that reductions in light attenuation were accompanied by stronger thermal stratification and greater hypolimnetic oxygen depletion. Lakes most affected by acidification experienced greater loss of water clarity during recovery relative to moderately acidified lakes. These findings are consistent with the hypothesis that lake acidification resulted in a reduction in light attenuation by CDOM resulting in greater water clarity in acidified lakes, and that this process has been reversed following regional declines in sulfate deposition.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Channel design is an important component of stream restoration, but little is known of the interplay between hydrogeomorphic features and ecosystem processes within designed channels. Water velocity, ...transient storage, and nutrient uptake were measured in channelized (prerestoration) and naturalized (postrestoration) reaches of a 1-km segment of Wilson Creek (KY) to assess the effects of restoration on mechanisms of nutrient retention. Stream restoration decreased flow velocity and reduced the downstream transport of nutrients. Median travel time was 50% greater in the restored channel due to lower reach-scale water velocity and the longer length of the meandering channel. Transient storage and the influence of transient storage on travel time were largely unaffected except in segments where backwater areas were created. First-order uptake rate coefficients for N and P were 30- and 3-fold higher (respectively) within the restored channel relative to its channelized state. Changes in uptake velocities were comparatively small, suggesting that restoration had little effect on biochemical demand. Results from this study suggest that channel naturalization enhances nutrient uptake by slowing water velocity. Solute injection experiments revealed differences in the functional properties of channelized, restored, and reference streams and provided a means for quantifying benefits associated with restoration of ecosystem services.
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IJS, KILJ, NUK, PNG, UL, UM
An analysis of multidecadal (1994–2021) temperature and dissolved oxygen profiles revealed a generally consistent pattern of response to climate change among oligotrophic lakes in the Adirondack ...Mountain region. Regional increases in annual average air temperature (0.34 ± 0.09 °C per decade) were accompanied by warming and thinning of epilimnia, cooling and expansion of hypolimnia, and declining hypolimnetic dissolved oxygen. Lakes in this region are recovering from acidification and we hypothesize that associated increases in dissolved color have caused greater heat trapping in the surface layer and earlier onset of stratification. The combined effects of increasing air temperature and declining water clarity resulted in stronger thermal stratification and greater oxygen depletion in bottom waters. Although the lakes were clustered in a relatively small geographic region, we found considerable interlake variability in trends for epilimnetic temperature (−0.06 to 0.66 °C decade
−1
), hypolimnetic temperature (−0.44 to 0.31 °C decade
−1
), and hypolimnetic oxygen (−55 to 0.7 µg L
−1
year
−1
). Lake bathymetry was a key variable determining the sensitivity of lakes to climate effects on oxygen resources. Lakes with thin hypolimnia exhibited low dissolved oxygen concentrations, which were exacerbated by strengthening of vertical temperature gradients and earlier onset of stratification. Photic depths are decreasing faster than mixing depths such that declines in photosynthesis may contribute to lower dissolved oxygen in deeper layers. We predict that with climate warming, fewer Adirondack lakes will provide suitable habitat for cold water fisheries such as brook trout due to decreasing hypolimnetic oxygen.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Upper estuarine segments are characterized by mixing of diverse source waters with a variety of constituents that may influence water clarity (e.g., algae, inorganic particulates, dissolved color). ...We measured turbidity, total suspended solids (TSS), chlorophyll-a (CHLa), dissolved organic carbon (DOC), and chromophoric dissolved organic matter (CDOM) in upper segments of the James and York Estuaries to better understand their role in light attenuation. Turbidity and TSS were found to be the best predictors of inter-site and intra-site variations in light attenuation. CHLa was not found to be a strong predictor of light attenuation, indicating that suspended particulate matter was largely non-algal. CDOM played a greater role in light attenuation in the Pamunkey and Mattaponi sub-estuaries, which derive a greater proportion of their inflow from lowland (Coastal Plain) sources where extensive wetlands and floodplain forest likely serve as a source of CDOM. Although dissolved and particulate components of light attenuation were derived from external (watershed) sources, variation in external inputs (river discharge) was not a strong predictor of estuarine light attenuation. Analysis of long-term (25-year) data indicate trends of decreasing turbidity and increasing water clarity at some sites, coinciding with decreases in river sediment inputs. In the James Estuary, underwater light conditions remain below targets for successful SAV colonization and favor phytoplankton-dominated primary production. Management actions that reduce sediment loads are likely to be the most effective means for improving water clarity in upper estuarine segments.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Liming, the application of carbonate materials (e.g., CaCO3, CaMg(CO3)2) to soils and surface waters, has been used extensively in Europe, and to a lesser extent in Canada and the United States, to ...mitigate the effects of acid deposition on forest and aquatic ecosystems. This literature review was conducted to assess the effects of liming on ecologically and economically important sugar maple dominated ecosystems of northeastern North America, where it is increasingly used to treat sugar maple dieback. Potential direct and indirect effects were considered to determine whether the use of liming to revitalize these forests could negatively affect other ecological parameters, including those in adjacent aquatic habitats. Based on current scientific literature, it is not anticipated that liming at rates of 1–3 t ha−1 would have major detrimental effects on these ecosystems. However, liming could have negative effects on northern hardwood forests with regard to earthworm invasions. The choice of liming as a mitigation tool should be made not only after weighing the potentially negative effects against the benefits of restoring sugar maple dominated stands in poorly buffered soils, but also after considering ecological components that could be lost or never recovered if an acidified forest ecosystem is not limed.
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BFBNIB, DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
•8-year study of harmful cyanobacteria in the James River.•Elevated microcystin associated with high water temperature and residence time.•Chlorophyll levels predict likelihood of exceeding ...microcystin thresholds.•Microcystin found in biota occurring in the oligohaline segment of the estuary.
We examined seasonal and longitudinal patterns in the occurrence of toxic cyanobacteria in the James River Estuary (Virginia). Highest chlorophyll and cyanobacteria levels were observed in the tidal freshwater segment, particularly during dry summers when freshwater replacement time was long. Cyanobacteria accounted for a small proportion of phytoplankton biomass (7–15%), and Microcystis comprised a small proportion of the cyanobacteria (<1%). Despite this, measureable levels of microcystin were commonly observed in water (>85% of samples in July, August and September), fish tissues (87% of planktivorous fishes) and shellfish (83% of individuals). Generic indicators of algal blooms (chlorophyll and algal biomass) had limited utility for predicting microcystin concentrations. However, chlorophyll was found to be a useful predictor for the probability of exceeding specific toxin thresholds. Tissue microcystin concentrations were highest in fish and shellfish collected from the tidal fresh segment, but were detectable in biota collected from the oligohaline at distances 50 km seaward.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Twenty-three station-years of diel oxygen data for the James River Estuary were analyzed to characterize longitudinal, seasonal, and interannual patterns of gross primary production (GPP) and ...ecosystem respiration (ER). We comparedtwo commonlyused methods for deriving metabolism (bookkeeping and Bayesian) to determine whether the observed patterns were robust with respect to computational methodology. The two methods revealed similar longitudinal patterns of increasing GPP and ER, and decreasing net ecosystem metabolism (NEM), with increasing salinity. Seasonal patterns in GPP and ER tracked water temperature and solar radiation, except during high discharge events when metabolism declined by 40%. The bookkeeping method yielded higher estimates of GPP and ER in the higher end of the range, and smaller estimates in the low end of the range, thereby accentuating seasonal and longitudinal differences. Inferences regarding net autotrophy and heterotrophy were robust, as both methods yielded positive estimates of NEM at the chlorophyll maximum (tidal fresh segment) and negative values for the saline portion of the estuary. Inferences regarding the relative importance of allochthonous inputs (based on inferred ER at GPP = 0) differed between the two methods. Values derived by the bookkeeping method indicated that respiration was largely supported by autochthonous production, whereas the Bayesian results indicated that autochthonous and allochthonous inputs were equally important. Overall, our findings show that methodological differences were small in the context of longitudinal, seasonal, and interannual variation but that the bookkeeping method yielded a wider range of values for GPP and ER relative to the Bayesian estimates.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The occurrence of harmful algal blooms has resulted in growing worldwide concern about threats to aquatic life and human health. Microcystin (MC), a cyanotoxin, is the most widely reported algal ...toxin in freshwaters. Prior studies have documented its presence in aquatic food webs including commercially important fish and shellfish. In this paper we present the first evidence that algal toxins propagate into riparian food webs. We show that MC is present in emerging aquatic insects (Hexagenia mayflies) from the James River Estuary and their consumers (Tetragnathidae spiders and Prothonotary Warblers, Protonotaria citrea). MC levels in Prothonotary Warblers varied by age class, with nestlings having the highest levels. At the site where nestlings received a higher proportion of aquatic prey (i.e., mayflies) in their diet, we observed higher MC concentrations in liver tissue and fecal matter. Warbler body condition and growth rate were not related to liver MC levels, suggesting that aquatic prey may provide dietary benefits that offset potential deleterious effects of the toxin. This study provides evidence that threats posed by algal toxins extend beyond the aquatic environments in which blooms occur.
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IJS, KILJ, NUK, PNG, UL, UM
Field trials were conducted to assess the potential for stocking native unionid mussels in urban streams of the Chesapeake Bay catchment. Juvenile, hatchery‐raised mussels were placed in enclosures ...at five urban streams (two restored and three unrestored) and two nearby rural streams. Adult mussels were translocated to two restored urban streams. Mussel growth and survivorship were assessed at the stream sites and for individuals maintained at hatchery ponds.
At all sites, water quality conditions were generally suitable for mussels with respect to temperature, pH, and dissolved oxygen. Food resources, as indicated by the quantity and quality of suspended and benthic particulate matter, were higher among rural sites and lower in unrestored urban streams.
Positive growth rates were observed at all sites, among both juveniles (caged) and translocated adults. Mussel fatty acid profiles were generally similar among sites, except for docosahexaenoic acid (DHA), which was lower among stocked mussels relative to mussels maintained at the hatchery.
Among the unrestored urban streams, the frequent occurrence of high discharge events resulted in burial and downstream loss of enclosures. At restored urban streams and rural streams, the washout effects were less severe. Apart from washout effects, mortality, as indicated by the presence of dead mussels, was low (<10%).
Overall, rural and restored urban streams provided suitable conditions for stocking native mussels, whereas in unrestored urban streams, bed and bank instability during high discharge events resulted in a high attrition of mussels. Conservation efforts may be aided by the consideration of mussel habitat needs in the design of stream restoration projects. The inclusion of mussel stocking efforts in urban stream restoration projects has the potential to facilitate stream recovery, expand and bring greater attention to mussel conservation efforts, and garner public support for the preservation of stream health in urban areas.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
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