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We compiled and examined 15 years (2002-2016) of high-frequency monitoring data from the National Estuarine Research Reserve System (NERRS) to characterize diel to interannual variability of pH and dissolved oxygen (DO, % saturation) across 16 diverse, shallow-water habitats along the US Atlantic, Gulf of Mexico, Caribbean, and Pacific coasts. We asked whether these systems exhibit a common pH/DO relationship, whether there were detectable interannual trends in temperature, pH, and DO within and across systems, and how pH/DO dynamics would relate to measured levels of nutrients and chlorophyll. Our analyses confirmed that large, metabolically driven, and thus concurrent fluctuations of pH and DO are a unifying feature of nearshore habitats. Moreover, we derived well-constrained relationships that predict (i) monthly mean pH or (ii) mean diel pH fluctuations across systems based on habitat mean salinity and (i) mean DO or (ii) mean diel DO fluctuations. This suggests that common metabolic principles drive diel to seasonal pH/DO variations within as well as across a diversity of estuarine environments. Yearly pH and DO anomalies did not show monotonous trends over the study period and differed considerably between sites and regions. However, weekly anomalies of means, diel minima, and diel ranges of pH and DO changed significantly over time and were strongly correlated to temperature anomalies. These general patterns lend strong empirical support to the notion that coastal acidification—in addition to being driven by eutrophication and atmospheric CO₂ increases—is exacerbated simply by warming, likely via increasing community respiration. Nutrient and chlorophyll dynamics were inversely related in these shallow, well-mixed systems, but higher nutrient levels were still associated with lower pH and lower DO levels in most, but not all, systems. Our analyses emphasize the particular dynamics of nearshore habitats and the critical importance of NERRS and its systemwide monitoring program.

Heatwaves are increasing in frequency, duration, and intensity in the atmosphere and marine environment with rapid changes to ecosystems occurring as a result. However, heatwaves in estuarine ecosystems have received little attention despite the effects of high temperatures on biogeochemical cycling and fisheries and the susceptibility of estuaries to heatwaves given their low volume. Likewise, estuarine heatwave co-occurrence with extremes in water quality variables such as dissolved oxygen (DO) and pH have not been considered and would represent periods of enhanced stress. This study analyzed 1440 station years of high-frequency data from the National Estuarine Research Reserve System (NERRS) to assess trends in the frequency, duration, and severity of estuarine heatwaves and their co-occurrences with atmospheric heatwaves, low DO, and low pH events between 1996 and 2019. Estuaries are warming faster than the open and coastal ocean, with an estuarine heatwave mean annual occurrence of 2 ± 2 events, ranging up to 10 events per year, and lasting up to 44 days (mean duration = 8 days). Estuarine heatwaves co-occur with an atmospheric heatwave 6–71 % of the time, depending on location, with an average estuarine heatwave lag range of 0–2 days. Similarly, low DO or low pH events co-occur with an estuarine heatwave 2–45% and 0–18% of the time, respectively, with an average low DO lag of 3 ± 2 days and low pH lag of 4 ± 2 days. Triple co-occurrence of an estuarine heatwave with a low DO and low pH event was rare, ranging between 0 and 7% of all estuarine heatwaves. Amongst all the stations, there have been significant reductions in the frequency, intensity, duration, and rate of low DO event onset and decline over time. Likewise, low pH events have decreased in frequency, duration, and intensity over the study period, driven in part by reductions in all severity classifications of low pH events. This study provides the first baseline assessment of estuarine heatwave events and their co-occurrence with deleterious water quality conditions for a large set of estuaries distributed throughout the USA.

Very high-resolution satellite imagery (≤5 m resolution) has become available on a spatial and temporal scale appropriate for dynamic wetland management and conservation across large areas. Estuarine wetlands have the potential to be mapped at a detailed habitat scale with a frequency that allows immediate monitoring after storms, in response to human disturbances, and in the face of sea-level rise. Yet mapping requires significant fieldwork to run modern classification algorithms and estuarine environments can be difficult to access and are environmentally sensitive. Recent advances in unoccupied aircraft systems (UAS, or drones), coupled with their increased availability, present a solution. UAS can cover a study site with ultra-high resolution (<5 cm) imagery allowing visual validation. In this study we used UAS imagery to assist training a Support Vector Machine to classify WorldView-3 and RapidEye satellite imagery of the Rachel Carson Reserve in North Carolina, USA. UAS and field-based accuracy assessments were employed for comparison across validation methods. We created and examined an array of indices and layers including texture, NDVI, and a LiDAR DEM. Our results demonstrate classification accuracy on par with previous extensive fieldwork campaigns (93% UAS and 93% field for WorldView-3; 92% UAS and 87% field for RapidEye). Examining change between 2004 and 2017, we found drastic shoreline change but general stability of emergent wetlands. Both WorldView-3 and RapidEye were found to be valuable sources of imagery for habitat classification with the main tradeoff being WorldView’s fine spatial resolution versus RapidEye’s temporal frequency. We conclude that UAS can be highly effective in training and validating satellite imagery.

Chlorophyll trends in subtropical and tropical estuaries are under characterized and may reveal patterns not shared by their temperate analogues. Detection of trends requires long-term monitoring programs, but these are uncommon. In this study, we utilized an 18-year chlorophyll- a time series from 2002 to 2020 in Weeks Bay, AL, to detect and quantify trends in chlorophyll variability over multiple time scales. Our analysis included up to 30 years of contemporaneous data for variables such as river discharge, nitrogen, and phosphorus to relate the chlorophyll- a trends to environmental drivers. We detected an abrupt shift in chlorophyll- a that was linked to changes in phosphorus and hydrology. The shift followed an abrupt increase in total phosphorus concentration from upstream of the primary river system that discharges into Weeks Bay. Total phosphorus continued to rise after the abrupt shift, but there was no detectable change in chlorophyll- a . We propose that the exceedance of a total phosphorus threshold at 0.1 mg l -1 , combined with a period of very low river discharge variability, induced the shift in chlorophyll- a . This shift opposed the pattern of proportional change usually observed as a result of nutrient enrichment. Not all monitoring stations underwent the abrupt shift, which demonstrated the complexity of phytoplankton response to environmental drivers and the significance of spatial differences even over small estuaries.

The existence of coastal ecosystems depends on their ability to gain sediment and keep pace with sea level rise. Similar to other coastal areas, Northeast Florida (United States) is experiencing rapid population growth, climate change, and shifting wetland communities. Rising seas and more severe storms, coupled with the intensification of human activities, can modify the biophysical environment, thereby increasing coastal exposure to storm-induced erosion and inundation. Using the Guana Tolomato Matanzas National Estuarine Research Reserve as a case study, we analyzed the distribution of coastal protection services–expressly, wave attenuation and sediment control–provided by estuarine habitats inside a dynamic Intracoastal waterway. We explored six coastal variables that contribute to coastal flooding and erosion–(a) relief, (b) geomorphology, (c) estuarine habitats, (d) wind exposure, (e) boat wake energy, and (f) storm surge potential–to assess physical exposure to coastal hazards. The highest levels of coastal exposure were found in the north and south sections of the Reserve (9% and 14%, respectively) compared to only 4% in the central, with exposure in the south driven by low wetland elevation, high surge potential, and shorelines composed of less stable sandy and muddy substrate. The most vulnerable areas of the central Reserve and main channel of the Intracoastal waterway were exposed to boat wakes from larger vessels frequently traveling at medium speeds (10–20 knots) and had shoreline segments oriented towards the prevailing winds (north-northeast). To guide management for the recently expanded Reserve into vulnerable areas near the City of Saint Augustine, we evaluated six sites of concern where the current distribution of estuarine habitats (mangroves, salt marshes, and oyster beds) likely play the greatest role in natural protection. Spatially explicit outputs also identified potential elevation maintenance strategies such as living shorelines, landform modification, and mangrove establishment for providing coastal risk-reduction and other ecosystem-service co-benefits. Salt marshes and mangroves in two sites of the central section (N-312 and S-312) were found to protect more than a one-quarter of their cross-shore length (27% and 73%, respectively) from transitioning to the highest exposure category. Proposed interventions for mangrove establishment and living shorelines could help maintain elevation in these sites of concern. This work sets the stage for additional research, education, and outreach about where mangroves, salt marshes, and oyster beds are most likely to reduce risk to wetland communities in the region.

In September of 2017, Hurricane Irma made landfall within the Rookery Bay National Estuarine Research Reserve of southwest Florida (USA) as a category 3 storm with winds in excess of 200 km h−1. We mapped the extent of the hurricane’s impact on coastal land cover with a seasonal time series of satellite imagery. Very high-resolution (i.e., <5 m pixel) satellite imagery has proven effective to map wetland ecosystems, but challenges in data acquisition and storage, algorithm training, and image processing have prevented large-scale and time-series mapping of these data. We describe our approach to address these issues to evaluate Rookery Bay ecosystem damage and recovery using 91 WorldView-2 satellite images collected between 2010 and 2018 mapped using automated techniques and validated with a field campaign. Land cover was classified seasonally at 2 m resolution (i.e., healthy mangrove, degraded mangrove, upland, soil, and water) with an overall accuracy of 82%. Digital change detection methods show that hurricane-related degradation was 17% of mangrove forest (~5 km2). Approximately 35% (1.7 km2) of this loss recovered one year after Hurricane Irma. The approach completed the mapping approximately 200 times faster than existing methods, illustrating the ease with which regional high-resolution mapping may be accomplished efficiently.

ContextThe relationship between native and non-native species richness is influenced by drivers including disturbance history and environmental character. Disturbance influences native-exotic richness relationships (NERRs) and results in positive or negative relationships, depending on its intensity. Land-use history can be used to understand how NERRs respond to disturbance and what mechanisms drive diversity.ObjectivesWe test the hypotheses that (1) native and nonnative plant species richness differ between land-use histories; (2) diversity is more strongly linked to environmental gradients in older forests than young stands, reflecting environmental sorting; (3) Native and non-native richness are positively correlated in older forests and negatively correlated in young forests.MethodsWe surveyed forests at Powdermill Nature Reserve in Southwestern Pennsylvania. We selected four replicates each of 40 to 70 year old second-growth forests with histories of mining, agriculture, and logging, and 14 older second-growth sites (>100 years) without recent human disturbance and collected presence data in a modified Whittaker plot design that included 1000, 100, 10, and 1-m2 subplots.ResultsNative and non-native richness were positively correlated in older forests, but uncorrelated in young stands. Proportions of non-native species were higher in mined and post-agricultural sites than in logged and old forests. Diversity-environment relationships were strongest in younger forests.ConclusionsDifferences in native and non-native richness between histories were strong enough to shift the direction of richness relationships in young forests. We conclude that differing impacts of land use on native (positive) and non-native (neutral) richness drive contrasting NERRs in forests with different histories.

Across the coastal zone, rates of carbon and nutrient exchange are defined by the spatiotemporal heterogeneity of individual estuarine systems. Elemental stoichiometry provides a mechanism for simplifying overlapping physical, chemical, and biological drivers into proxies that can be used to compare and monitor estuarine biogeochemistry. To this end, the seasonal and tidal variability of estuarine stoichiometry was examined over an annual cycle in North Inlet (NI), South Carolina. Surface samples for dissolved and particulate carbon (C), nitrogen (N), and phosphorus (P) were collected every 20 days (August 2014 to August 2015) over a semidiurnal tidal cycle. Dissolved nutrient flux estimates of an individual tidal creek were also made. Overall, the results demonstrated the dominance of seasonal versus tidal forcing on water column C:N:P stoichiometry. This seasonal behavior mediated the relative exchange of N and into and out of the tidal creek and influenced the nutrient status index (NSI) of NI plankton communities. These communities were largely N deficient with the magnitude of this deficiency impacted by assumptions of inorganic versus organic plankton demand and nutrient supply. Persistent N deficiency appeared to help drive the net import of N, while temporary P surplus likely drives its seasonal export. Combined, these results indicate that material delivery must be considered on seasonal time frames, as net annual fluxes do not reflect the short-term deliveries of C and nutrients into nearshore ecosystems.

Grand Bay National Estuarine Research Reserve (NERR) is an important ecosystem in the Mississippi Gulf Coast. It serves as important nursery areas for juveniles of many species of fish. The bay is also used for fishing, crabbing, oyster togging, boating as well as recreation. Like in other aquatic environments, this bay may be contaminated by microorganisms including pathogenic bacteria. The objective of this study was to evaluate the microbiological quality of water in the Grand Bay NERR and determine the levels and potential source(s) of human fecal pollution. To achieve this goal, water samples were collected aseptically every month in Bayou Heron, Bayou Cumbest, Point Aux Chenes Bay and Bangs Lake. Enterococci were concentrated from water samples by membrane filtration according to the methodology outlined in USEPA Method 1600. After incubation, DNA was extracted from bacteria colonies on the membrane filters by using QIAamp DNA extraction kit. Water samples were also tested for the presence of traditional indicator bacteria including: heterotrophic plate count, total coliforms, fecal coliforms, and Enterococcus bacteria. The marker esp gene was detected in one site of Bayou Cumbest, an area where human populations reside. Data from this study indicates higher concentrations of indicator bacteria compared to the recommended acceptable levels. Presence of esp marker and high numbers of indicator bacteria suggest a public health concern for shellfish and water contact activities. Hence, control strategies should be developed and implemented to prevent further contamination of the Grand bay NERR waters.

Evaluations of tidal wetland restoration efforts suffer from a lack of appropriate reference sites and standardized methods among projects. To help address these issues, the National Estuarine Research Reserve System (NERRS) and the NOAA Restoration Center engaged in a partnership to monitor ecological responses and evaluate 17 tidal wetland restoration projects associated with five reserves. The goals of this study were to (1) determine the level of restoration achieved at each project using the restoration performance index (RPI), which compares change in parameters over time between reference and restoration sites, (2) compare hydrologie and excavation restoration projects using the RPI, (3) identify key indicator parameters for assessing restoration effectiveness, and (4) evaluate the value of the NERRS as reference sites for local restoration projects. We found that the RPI, modified for this study, was an effective tool for evaluating relative differences in restoration performance; most projects achieved an intermediate level of restoration from 2008 to 2010, and two sites became very similar to their paired reference sites, indicating that the restoration efforts were highly effective. There were no differences in RPI scores between hydrologie and excavation restoration project types. Two abiotic parameters (marsh platform elevation and groundwater level) were significantly correlated with vegetation community structure and thus can potentially influence restoration performance. Our results highlight the value of the NERRS as reference sites for assessing tidal wetland restoration projects and provide improved guidance for scientists and restoration practitioners by highlighting the RPI as a trajectory analysis tool and identifying key monitoring parameters.