Davis Pond Research Articles

Impact of freshwater diversions on vegetation in coastal wetlands based on remote sensing derived vegetation index

There exist contrasting results on the impact of large-scale freshwater and sediment diversions on land gain/loss. To improve understanding on the efficacy of diversion projects in restoring coastal wetlands, we aim to evaluate the long-term impacts of diversion-altered salinity and water level on vegetation productivity in coastal wetlands. Two freshwater diversion projects Caernarvon and Davis Pond in Louisiana, U.S. and associated reference sites were selected for inclusion in this study. We implemented multi-level Bayesian models to evaluate 1) how vegetation productivity approximated by Landsat-derived Normalized Difference Vegetation Index (NDVI) in peak biomass season changed over time (pre- and post-construction and operation of the freshwater diversions), and 2) how peak-season NDVI responded to mean and variability of water level and salinity among a suite of factors that could affect vegetation productivity. Analysis showed difference in temporal trends of NDVI between the reference and diversion site for the Caernarvon project with a significant increase at the diversion site although NDVI negatively responded to diversion at the beginning. Diversion did not seem to negatively affect NDVI for the Davis Pond project and NDVI only marginally increased at the diversion site. For both projects, NDVI negatively responded to water level, while salinity negatively affected NDVI or showed quadratic relation with NDVI. At the Caernarvon diversion project, the negative impact of water level on NDVI was greater at the diversion site than at the reference site. At the Davis Pond project, it was the salinity that showed different impact between the diversion and reference site. The temporal increase of NDVI at the Caernarvon diversion site can be explained by the lower salinity driven by diversion. The quadratic relation between salinity and NDVI at the Davis Pond diversion project led to only marginal increase at the diversion site. This study provided uncertainty estimates in temporal trend of NDVI and the impact of two key abiotic drivers on NDVI. The improved understanding on vegetation productivity will help predict landscape change in response to freshwater diversions.

Coastal wetland area change for two freshwater diversions in the Mississippi River Delta

Coastal systems around the globe are being re-integrated with adjacent river systems to restore the natural hydrologic connection to riparian wetlands. The Mississippi River sediment diversions or river reconnections are one such tool to combat high rates of wetland loss in coastal Louisiana, USA by providing freshwater, sediment, and nutrients. There has been some disagreement in the published literature whether re-establishing river reconnection is slowing or contributing to coastal wetland loss. This issue is due to the difficulties in the application of remote sensing in low-relief environments where water level changes could indicate either land loss or simply temporary submergence. We analyzed land change at the receiving areas of two existing freshwater river diversions, Davis Pond and Caernarvon, which have been intermittently receiving river water for up to 2+ decades. This study provides a robust analysis of wetland land change rates in proximity these river diversions including years before river reconnection. Our analyses indicate a net land gain since river reconnection operations began at Davis Pond Diversion (+3.42 km2; range: +2.02–4.81 km2) and no statistically significant change at the Caernarvon Diversion. The Davis Pond wetland results are corroborated with data from a decadal field study documenting increased inorganic sedimentation in the soil. It is clear from this study and others, that river reconnection can increase or, in the case of Caernarvon, have no statistical effect on the land change in these systems due to differences in vegetation, hydroperiod, sediment delivery and external factors including hurricane impacts. Our remote sensing analysis was compared with a global water area change analysis mapping tool which also supported our findings.

Mass removal efficiencies in water and consequences after a river diversion into coastal wetlands: second thoughts

Salinity control, nutrient additions, and sediment supply were directly or indirectly the rationale for a $220 million coastal wetland restoration project (Davis Pond River Diversion) that began in 2002. We sampled Mississippi River water going in and out of the receiving basin from 1999 to 2018 to understand why wetland loss increased after it began. There was a reduction in inorganic sediments, nitrogen (N), and phosphorus (P) concentrations within the ponding area of 77%, 39% and 34%, respectively, which is similar to that in other wetlands. But the average sediment accumulation of 0.6 mm year−1 inadequately balances the present-day 5.6 mm year−1 sea level rise or the 7.9 ± 0.13 mm year−1 accretion rates in these organic soils. Nutrients added likely reduced live belowground biomass and soil strength, and increased decomposition of the organic matter necessary to sustain elevations. The eutrophication of the downstream aquatic system from the diversion, principally by P additions, increased Chl a concentrations to a category of ‘poor’ water quality. We conclude that this diversion, if continued, will be a negative influence on wetland area and will eutrophy the estuary. It is a case history example for understanding the potential effects arising from proposed river diversions.

Dynamic Energy Budget modelling to predict eastern oyster growth, reproduction, and mortality under river management and climate change scenarios

Eastern oysters growing in deltaic Louisiana estuaries in the northern Gulf of Mexico must tolerate considerable salinity variation from natural climate variability (e.g., rainfall and stream run-off pushing isohalines offshore; tropical storms pushing isohalines inshore) and man-made diversions and siphons releasing freshwater from the Mississippi River. These salinity variations are predicted to increase with future climate change because of the increased frequency of stronger storms and also in response to proposed large-scale river diversions. Increased Mississippi River flow into coastal estuaries from river diversions, along with potential changes in rainfall and stream run-off from climate change will alter spatial and temporal salinity patterns. In this study we used an individual Dynamic Energy Budget model to predict growth and reproductive potential of eastern oysters across observed and simulated salinity gradients corresponding to different climate and river management scenarios. We used validated model outputs of salinity from a coupled hydrology-hydrodynamic model to assess the current impacts of Davis Pond diversion discharge on oysters located downstream. Under a high diversion discharge scenario oyster growth potential was reduced by 9%, 4%, and 1% in Upper, Mid, and Lower Bay locations, respectively, as compared to a limited discharge year. Reproductive outputs decreased by 34% and 2% in the Upper and Lower Bay locations, respectively, and increased by 2% at the Mid Bay site. In scenarios combining predicted increased temperature with the effect of diversions, all oysters located in the Upper and Mid Bay sites died due to severe summer conditions (high temperatures combined with low salinity). Overall, oysters in down-estuary locations, influenced by both estuarine river management and gulf conditions demonstrated significant tolerance to changing salinity and temperature conditions from diversions alone and when combined with climate change. In contrast, oysters located up-estuary, and exposed to more extreme salinity impacts from river management, demonstrated potentially lethal impacts through direct mortality, and reduced sustainability through decrease in reproductive output. These predictions at the individual level may translate into less sustainable populations in the most extreme scenarios; restoration and production plans may benefit from accounting for these impacts on reproductive output particularly as decision makers seek to restore critical oyster areas.

Multivariate Analyses of Water Quality Dynamics Over Four Decades in the Barataria Basin, Mississippi Delta

Here we examine a combined dataset of water quality dynamics in the Barataria Basin, Louisiana based on transect studies from 1977 to 1978 (Seaton) and from 1994 to 2016. The Davis Pond river diversion into Lake Cataouatche began discharging Mississippi River water into the mid-basin in 2005, and so the later dataset was divided in Pre- and Post-diversion periods. The stations from these three datasets (Seaton, Pre- and Post-diversion) were combined into eleven station groupings for statistical analysis that included ANOVA and principal component analysis. In addition, Trophic State Index (TSI) scores were calculated for each grouping during the three time periods. Lake Cataouatche changed the most with the opening of the Davis Pond river diversion, becoming clearer and less eutrophic with addition of river water, which passed through a large wetland area where sediments were retained before entering the lake. The TSI results for the Seaton re-analysis were very similar to the original analysis and to that of the Pre- and Post-diversion datasets, indicating that the trophic status of the basin waters has remained relatively unchanged. The upper-basin has remained eutrophic with degraded water quality while the lower-basin has remained more mesotrophic without significant water quality deterioration. A main cause of water quality deterioration is agricultural runoff and pervasive hydrologic alteration that bypasses wetlands and causes most runoff to flow directly into water bodies.

Spatial and temporal changes to a hydrologically-reconnected coastal wetland: Implications for restoration

Mississippi River Delta wetlands were isolated from river influence due to levee construction beginning in the early 1900's. Surface water diversions were primarily designed to manage salinity and maintain marsh vegetation by reintroducing Mississippi River water and nutrients into adjacent wetlands. Phosphorus (P) is a major limiting nutrient that can control productivity, but in excess can contribute to wetland eutrophic conditions and water quality degradation. Most wetland soil characterization assessments consider soil total P, however, this parameter alone cannot describe P bioavailability due to differences in organic and inorganic forms. A soil characterization of the Davis Pond diversion was done in 2007, before full-scale operation began, and in 2018 after 11 years of river loading. The top 10 cm of soil from 140 stations each year were analyzed for physiochemical properties and both organic and inorganic P forms. Mineral content is used to delineate areas of river diversion influence and compare P stocks between hydrologically isolated marsh areas and where effective river diversion reconnection took place. The river diversion resulted in a nearly 100% increase in soil mineral content and 58% increase in bulk density. The dominant source of soil P has changed from organic P to inorganic P in 29% of the wetland area, significantly associated with mineral content of the soil. Inorganic P stocks in diversion influenced areas are 9 times higher than those which remained isolated from riverine materials. The study demonstrates that long-term addition of mineral sediments and inorganic P did not lead to deleterious effects in the wetland soil. This is the first study in the Mississippi River delta to spatially track river reconnection driven wetland P dynamics and can provide valuable information for predictive models for sediment diversions for coastal restoration.

Net land gain or loss for two Mississippi River diversions: Caernarvon and Davis Pond

Coastal wetland restoration can be complex and expensive, so knowing long‐term consequences makes it important to inform decisions about if, when, and where to conduct restoration. We determined temporal changes in land gain and loss in receiving basins and adjacent reference areas for two diversions of the Mississippi River in south Louisiana (Davis Pond and Caernarvon initiated in 1991 and 2002, respectively). Water from both diversions went into receiving basins with vegetated areas as did the adjoining reference areas. The results from two different types of satellite imagery analyses demonstrate a net land loss after diversions began. The results were confirmed for the Caernarvon diversion using a before–after/control–impact analysis of independently collected data over a larger area of the estuary. These results are consistent with an analysis of land gain and loss after a natural levee break on the Mississippi River in 1973. The positive influences of adding new sediments were apparently counter‐balanced by other factors, and consistent with the conclusion from other studies indicating that increased nutrient supply and flooding are, by themselves, negative influences on marsh health. Modeling the ecosystem effects of diversions can be calibrated and tested using landscape‐scale analyses like this to understand the chronic and delayed effects, including the unintended consequences. Basing the legitimacy of river diversion on ecosystem modeling will be premature without successfully reproducing empirical results like these in ecosystem models.

Multi-decadal trends and influences on dissolved organic carbon distribution in the Barataria Basin, Louisiana from in-situ and Landsat/MODIS observations

Barataria Basin, a deltaic marsh-estuary system in the northern Gulf of Mexico (nGOM), is an important source of dissolved organic matter (DOM) to the coastal ecosystem. To assess DOM dynamics, monthly measurements of dissolved organic carbon (DOC) concentrations and colored DOM (CDOM; an optical proxy for DOC) absorption were obtained over a three-year period (2008–2011) along a transect encompassing the upper, middle and lower regions of the Barataria Basin estuary. While CDOM absorption coefficient at 355 nm (ag355) generally decreased and spectral slope at 275–295 nm (S275–295) increased along the transect from the upper to lower basin, deviations were observed associated with hydrologic and meteorological influences. An application of wavelet analysis to the time-series of ag355 and various freshwater sources revealed a spatiotemporal resonance of ag355 with freshwater input from the Mississippi River (MR), the controlled freshwater discharge from the Davis Pond freshwater diversion, and rainfall in the lower, middle and upper basins, respectively. Field measurements and Landsat/MODIS data spanning across different seasons between 2008 and 2011 were used to develop optimized ag355 empirical algorithms for the high river flow, cold front, and normal conditions. Power law models relating a band ratio (green/red) of a satellite sensor to ag355 showed good performance for the MODIS-Aqua (R2~0.81–0.83, N = 581) and Landsat-5 TM (R2~0.72–0.79, N = 304) imagery. ag355-DOC relationships (R2~0.77–0.84, N = 306) applied to historical Landsat-5 TM (1985–2011) and MODIS-Aqua imagery (2002−2012) showed strong environmental influences on multi-decadal CDOM and DOC spatiotemporal trends. Satellite-derived DOC agreed reasonably well with in-situ measured DOC (averaged R2 = 0.71; RMSE = 2.13). While the time-series DOC showed seasonality and decreasing gradients from the upper to lower basin, an overall increase in DOC was observed in the upper and middle basins from 1985 to 2012. However, in the lower basin, DOC increased from 1985 to 2006 but decreased from 2007 to 2012, likely due to the impact of two major hurricanes in 2005. Furthermore, relationships between satellite-derived DOC and land cover variations (1985–2011) along the wetland-estuary interfaces derived from Landsat-5 TM supervised classification showed an increase in DOC with corresponding increase in developed area in the upper basin, while in the lower basin, DOC increased by 41% (R2 = 0.54) between 1985 and 2006 corresponding to a 17% decrease in salt marsh area, suggesting strong land use/land loss impact on the long-term DOC trends in Barataria Basin.

Hydrodynamic controls on sediment retention in an emerging diversion-fed delta

The morphodynamics of river-dominated deltas are largely controlled by the supply and retention of sediment within deltaic wetlands and the rate of relative sea-level rise. Yet, sediment budgets for deltas are often poorly constrained. In the Mississippi River Delta, a system rapidly losing land due to natural and anthropogenic causes, restoration efforts seek to build new land through the use of river diversions. At the Davis Pond Freshwater Diversion, a new crevasse splay has emerged since construction was completed in 2002. Here, we use beryllium-7 activity in sediment cores and USGS measurements of discharge and turbidity to calculate seasonal sediment input, deposition, and retention within the vegetated Davis Pond receiving basin. In winter/spring 2015, which included an experimental period of high discharge through the diversion, Davis Pond received 106,800 metric tons of sediment, 44% of which was retained within the basin. During this time, mean flow velocity was 0.21 m s−1 and mean turbidity was 56 formazin nephelometric units (FNU). In summer/fall 2015, the Davis Pond basin received 35,900 metric tons of sediment, 81% of which was retained. Mean flow velocity in summer/fall was 0.10 m s−1 and mean turbidity was 55 FNU. The increase in sediment retention from winter/spring 2015 to summer/fall 2015 may be due in part to the corresponding drop in water flow velocity, which allowed more sediment to settle out of suspension. Although high water discharge increases sediment input and deposition, increased turbulence associated with higher current velocity appears to increase sediment throughput and thereby decrease the sediment trapping efficiency. Sediment retention in Davis Pond is on the high end of the range seen in deltaic wetlands, perhaps due to the enclosed geometry of the receiving basin. Future diversion design and operation should target moderate water discharge and flow velocities in order to jointly maximize sediment deposition and retention and provide optimal conditions for delta growth.

Wetland Plant Community Responses to the Interactive Effects of Simulated Nutrient and Sediment Loading: Implications for Coastal Restoration Using Mississippi River Diversions

The Mississippi River Delta Complex (MRDC) has experienced extensive wetland loss in the last century due, in part, to flood control levees that have isolated the lower Mississippi River and its sediment resource from adjacent wetlands. Reconnecting the River to these wetlands through diversions is being used and proposed on a larger scale for the future, to reduce wetland loss rates. However, some currently operating diversions (e.g., Caernarvon and Davis Pond) have been implicated in causing negative impacts on wetland ecosystem structure and function due to increased nutrient loads in diverted Mississippi River water combined with insufficient sediment delivery. Initial assessments of these concerns were carried out in a greenhouse setting where six nutrient enrichment treatment levels (control, NO3, NH4, PO4, SO4, and Combo [NO3 + NH4 + PO4 + SO4]) were applied with and without sediment addition to 60 marsh sods from a Sagittaria lancifolia-dominated oligohaline wetland at rates simulating the Davis Pond Diversion of the Mississippi River. After 25 months, independent enrichment with N (regardless of form) and sediment was generally beneficial to wetland structure and function, while SO4 enrichment had the opposite effect, regardless of sediment addition. Simultaneous application of N and P (i.e., the Combo treatment level) ameliorated the negative impacts of SO4-loading, but the concurrent application of sediment did not, likely because the loading rate was based on a diversion that was designed to deliver water and not to maximize sediment input. Nonetheless, sediment input is critical to the sustainability of MRDC wetlands experiencing high rates of deterioration. Thus, optimizing future diversions to maximize sediment delivery, along with continued surveillance of negative nutrient effects, are recommended management decisions.

Assessing methods for estimating roughness coefficient in a vegetated marsh area using Delft3D

A Delft3D-FLOW model was used to simulate tidal flow in Davis pond marsh in Louisiana, USA. The study area is a freshwater marsh consisting of one main channel and floodplain. Vegetation-induced flow resistance greatly influences tidal flow dynamics in the marsh. This study evaluated eight approaches to estimate vegetation roughness, including two constant Manning's n values, four empirical relations for calculating n, and two methods for calculating Chezy's C values originally embedded in the Delft3D model. Simulated results of water surface elevation (WSE) were compared with the corresponding field observation at eleven stream gauges in the study area. We concluded that the roughness coefficient for vegetated area varies with time as flow depth changes. Among the selected empirical relations for the vegetation roughness, the ones accounting for the effect of the vegetation frontal area and the degree of submergence have closely matched the measurements.

Seasonal Variation of Colored Dissolved Organic Matter in Barataria Bay, Louisiana, Using Combined Landsat and Field Data

Coastal bays, such as Barataria Bay, are important transition zones between the terrigenous and marine environments that are also optically complex due to elevated amounts of particulate and dissolved constituents. Monthly field data collected over a period of 15 months in 2010 and 2011 in Barataria Bay were used to develop an empirical band ratio algorithm for the Landsat-5 TM that showed a good correlation with the Colored Dissolved Organic Matter (CDOM) absorption coefficient at 355 nm (ag355) (R2 = 0.74). Landsat-derived CDOM maps generally captured the major details of CDOM distribution and seasonal influences, suggesting the potential use of Landsat imagery to monitor biogeochemistry in coastal water environments. An investigation of the seasonal variation in ag355 conducted using Landsat-derived ag355 as well as field data suggested the strong influence of seasonality in the different regions of the bay with the marine end members (lower bay) experiencing generally low but highly variable ag355 and the freshwater end members (upper bay) experiencing high ag355 with low variability. Barataria Bay experienced a significant increase in ag355 during the freshwater release at the Davis Pond Freshwater Diversion (DPFD) following the Deep Water Horizon oil spill in 2010 and following the Mississippi River (MR) flood conditions in 2011, resulting in a weak linkage to salinity in comparison to the other seasons. Tree based statistical analysis showed the influence of high river flow conditions, high- and low-pressure systems that appeared to control ag355 by ~28%, 29% and 43% of the time duration over the study period at the marine end member just outside the bay. An analysis of CDOM variability in 2010 revealed the strong influence of the MR in controlling CDOM abundance in the lower bay during the high flow conditions, while strong winds associated with cold fronts significantly increase CDOM abundance in the upper bay, thus revealing the important role these events play in the CDOM dynamics of the bay.

Three-Dimensional Hydrodynamic Simulation of Tidal Flow through a Vegetated Marsh Area

AbstractSimulation of tidal flow in an estuarine marsh area is challenging because of resistance from spatially and temporally varied vegetation. This study simulated the tidal flow in the Davis Pond marsh area near New Orleans, Louisiana, using an open source program. To quantify the time-varying roughness coefficient, four empirical equations for calculating Manning’s roughness coefficient were incorporated into the program in addition to two options offered by the program to calculate the Chezy’s coefficient and one option to use the modified momentum equations and the k−ϵ turbulence model. Results showed that the time-varying roughness coefficient equations accounting for both the degree of submergence and the vegetation frontal area gave the closest matches with the observed data.

Hydrologic remediation for the Deepwater Horizon incident drove ancillary primary production increase in coastal swamps

AbstractAs coastal wetlands subside worldwide, there is an urgency to understand the hydrologic drivers and dynamics of plant production and peat accretion. One incidental test of the effects of high rates of discharge on forested wetland production occurred in response to the 2010 Deepwater Horizon incident, in which all diversions in Louisiana were operated at or near their maximum discharge level for an extended period to keep offshore oil from threatened coastal wetlands. Davis Pond Diversion was operated at six times the normal discharge levels for almost 4 months, so that Taxodium distichum swamps downstream of the diversion experienced greater inundation and lower salinity. After this remediation event in 2010, above‐ground litter production increased by 2.7 times of production levels in 2007–2011. Biomass of the leaf and reproductive tissues of several species increased; wood litter was minimal and did not change during this period. Root production decreased in 2010 but subsequently returned to pre‐remediation values in 2011. Both litter and root production remained high in the second growing season after hydrologic remediation. Annual tree growth (circumference increment) was not significantly altered by the remediation. The potential of freshwater pulses for regulating tidal swamp production is further supported by observations of higher T. distichum growth in lower salinity and/or pulsed environments across the U.S. Gulf Coast. Usage of freshwater pulses to manage altered estuaries deserves further consideration, particularly because the timing and duration of such pulses could influence both primary production and peat accretion. © 2015 The Authors. Ecohydrology published by John Wiley & Sons Ltd.

First Recorded Occurrence ofOncorhynchus mykiss(Rainbow Trout) in Louisiana

An individual of Oncorhynchus mykiss (Rainbow Trout) was collected in a diversion canal of the Mississippi River known as Davis Pond located at river kilometer (RKM) 191.03 in St. Charles Parish near Luling, LA. This locality is the southern-most record for Rainbow Trout in the Mississippi River Basin and represents a range extension of 733.5 RKM south from the previous southern-most locality at Lake Whittington, Bolivar County, MS. The collection we report here also represents the first documented record of Rainbow Trout in Louisiana.

Freshwater diversions as an ecosystem management tool for maintaining soil organic matter accretion in coastal marshes

Abstract Marsh soil accretion processes were examined at 12 locations in fresh and brackish marshes in Louisiana's northern Barataria Basin estuary. Soil accretion rate determined from 137 Cs ranged from 0.59 to 1.03 cm yr − 1 . Soil structure and accretion were controlled primarily by organic matter accumulation rather than mineral sediment deposition with water and entrapped gases occupying the majority of the soil volume ranging from 92 to 95%. Organic matter accumulation ranged from 328 to 580 g m − 2 yr − 1 while mineral accumulation ranged from 78 to 380 g m − 2 yr − 1 Such organic-based fresh and brackish marsh soil are more fragile than mineral based marsh soils and are subject to impact by salt water intrusion and hurricane storm surge forces. The Davis Pond diversion is a conduit between the Mississippi River and the coastal marshes of Barataria basin currently reintroducing river water into the basin leading to lower basin salinities This hydrologic management measure should benefit and extend the stability of the studied marsh sites encouraging continued vegetation growth and soil organic matter accumulation. Accrual of organic matter is necessary to prevent drowning of the marsh which is subject to both the global eustatic sea level rise (1–2 mm yr − 1 ) and significant local subsidence (~ 10 mm yr − 1 ). This high rate of relative sea level rise can lead to open water/ponding and subsequent erosion of the surrounding marsh due to flooding and salinity stress.

Impacts of Mississippi River diversions on salinity gradients in a deltaic Louisiana estuary: Ecological and management implications

Large-scale river diversions on the lower Mississippi River are considered to be an important component of wetland restoration efforts in coastal Louisiana. Diversions are used primarily for salinity control but increasingly proposed also as a major way to deliver sediments and nutrients to coastal wetlands impacted by the construction of flood control levees. We used a coupled hydrology–hydrodynamics model of the Barataria estuary, a site of the Davis Pond Diversion – the world's largest river diversion project, to examine salinity variations under different diversion discharge scenarios. Discharge scenarios were selected based on actual freshwater discharges in different years and management alternatives that included a scenario with several new diversions. The model results indicate that river diversions strongly affect salinities only in the middle section of the Barataria estuary. The upper parts of the estuary are fresh most of the time and so the excess fresh water from river diversions has only a minor impact on salinity in this region. Also, the Davis Pond diversion has little impact on salinities in the coastal section of the estuary because of strong marine influence in this area adjacent to the Gulf of Mexico. Interestingly, the predicted salinity differences between different model scenarios can be as high as 10 in some months and places. These differences can be biologically significant depending on the salinity tolerance of different species and could cause a shift in community composition within the affected region.

A Geostatistical Analysis of Soil Properties in the Davis Pond Mississippi Freshwater Diversion

Land loss has been a major concern in the Mississippi River Delta as the levees constructed along the river caused a severe drop in sediment and nutrient loads for the adjacent wetland areas. Several freshwater diversions along the lower reach of the Mississippi River were built to resolve this. This study represents the first spatial survey of one such diversion, Davis Pond, with the objective to understand the current nutrient status and to determine a baseline of key soil properties. We also expect that the processes driving wetland accretion are scale dependent, and present the scale dependency in the spatial relationships of those properties which are key to accretion. These soil properties are: soil moisture (MOIST), bulk density (BD), pH, organic matter content (OM), total phosphorus (TP), nitrogen (TN), and carbon (TC) sampled 142 stations (0–10 and 10–20‐cm depth). Maps of soil properties in the recently accreted 0‐ to 10‐cm interval were produced using kriging. From the spatial correlation analysis we observed that TN, TC, and OM, in the 0‐ to 10‐cm depth interval, had similar spatial properties and were closely related to BD. The spatial relationship between TP or pH with any other variable was weak. We also inferred that processes driving dynamics of TP in the Davis Pond act on a finer spatial scale than processes affecting TN, TC, and OM. We can identify where there are different deposition processes affecting the spatial patterns in this wetland, that is, C deposition by the plants vs. mineral river sediment deposition.

Impacts of diverted freshwater on dissolved organic matter and microbial communities in Barataria Bay, Louisiana, U.S.A.

Here we present results of an initial assessment of the impacts of a water diversion event on the concentrations and chemical composition of dissolved organic matter (DOM) and bacterioplankton community composition in Barataria Bay, Louisiana U.S.A, an important estuary within the Mississippi River Delta complex. Concentrations and spectral properties of DOM, as reflected by UV/visible absorbance and fluorescence, were strikingly similar at 26 sites sampled along transects near two western and two eastern areas of Barataria Bay in July and September 2010. In September 2010, dissolved organic carbon (DOC) was significantly higher (568.1–1043 μM C, x = 755.6 +/− 117.7 μM C, n = 14 ) than in July 2010 (249.1–577.1 μM C, x = 383.7 +/− 98.31 μM C, n = 14); conversely, Abs 254 was consistently higher at every site in July (0.105–0.314) than in September (0.080–0.221), averaging 0.24 ± 0.06 in July and 0.15 ± 0.04 in September. Fluorescence data via the fluorescence index (FI 450/500) revealed that only 30% (8 of 26) of the July samples had an FI 450/500 above 1.36, compared to 96% (25 of 26) for the September samples. This indicates a more terrestrial origin for the July DOM. Bacterioplankton from eastern sites differed in composition from bacterioplankon in western sites in July. These differences appeared to result from reduced salinities caused by the freshwater diversion. Bacterioplankton communities in September differed from those in July, but no spatial structure was observed. Thus, the trends in bacterioplankton and DOM were likely due to changes in water masses (e.g., input of Mississippi River water in July and a return to estuarine waters in September). Discharge of water from the Davis Pond Freshwater Diversion (DPFD) through Barataria Bay may have partially mitigated some adverse effects of the oil spill, inasmuch as DOM is concerned.

Repeated century-scale droughts over the past 13,000 yr near the Hudson River watershed, USA

Long-term sediment and ground-penetrating radar data from Davis Pond, a small lake near the Hudson River valley, reveal past droughts in a historically humid region that presently supplies water to millions of people in and around New York City. A minimum of eleven sandy paleoshoreline deposits in the lake date from 13.4 to 0.6 cal ka BP. The deposits span 1500 to 200 yr between bracketing radiocarbon ages, and intrude into lacustrine silts up to 9.0 m below the modern lake surface in a transect of six sediment cores. Three low stands, ca. 13.4–10.9, 9.2 and 8.2 cal ka BP indicate low regional moisture balance when low temperatures affected the North Atlantic region. Consistent with insolation trends, water levels rose from ca. 8.0 cal ka BP to present, but five low stands interrupted the rise and are likely associated with ocean–atmosphere interactions. Similar to evidence from other studies, the data from Davis Pond indicate repeated multi-century periods of prolonged or frequent droughts super-imposed on long-term regional trends toward high water levels. The patterns indicate that water supplies in this heavily populated region have continuously varied at multiple time scales and confirm that humid regions such as the northeastern United States are more prone to severe drought than historically expected.