DOI: 10.5061/dryad.cjsxksncr
title: Climate and vegetation change in a coastal marsh: two snapshots of groundwater dynamics and tidal flooding at Piermont Marsh, NY spanning 20 years

description: Groundwater hydrology plays an important role in coastal marsh
 biogeochemical function, in part because groundwater dynamics drive the
 zonation of macrophyte community distribution. Changes that occur over
 time, such as sea level rise and shifts in habitat structure are likely
 altering groundwater dynamics and eco-hydrological zonation. We examined
 tidal flooding and marsh water table dynamics in 1999 and 2019 and mapped
 shifts in plant distributions over time, at Piermont Marsh, a brackish
 tidal marsh located along the Hudson River Estuary near New York City. We
 found evidence that the marsh surface was flooded more frequently in 2019
 than in 1999, and that tides were propagating further into the marsh in
 2019, although marsh surface elevation gains were largely matching that of
 sea level rise. The changes in groundwater hydrology that we observed are
 likely due to the high tide rising at a rate that is greater than that of
 mean sea level. In addition, we reported on changes in plant cover by P.
 australis, which has displaced native marsh vegetation at Piermont Marsh.
 Although P. australis has increased in cover, wrack deposition and plant
 die off associated Superstorm Sandy allowed for native vegetation to
 rebound in part of our focus area. These results suggest that climate
 change and plant community composition may interact to shape ecohydrologic
 zonation. Considering these results, we recommend that habitat models
 consider tidal range expansion and groundwater hydrology as metrics when
 predicting the impact of sea level rise on marsh resilience.
description: Hydrological measurements were collected during the spring and
 summer of 1999 and 2019 in Piermont Marsh (coordinates 41.0361°,
 -73.9105°). These measurements covered a transect that was laid out
 perpendicular to a tidal channel. The objective of this study was to
 compare the current tidal flooding and groundwater table levels with the
 data from 1999. The goal was to assess the differences in tidal hydrology
 between these two distinct time periods, which also differed in terms of
 marsh and water level elevations. To determine
 groundwater levels and tidal flooding across the marsh, we installed seven
 water level loggers along a gradient, ranging from the tidal channel to
 the upland area. We constructed wells by suspending pressure transducers
 within 7.5 cm diameter perforated PVC pipes lined with screening to
 prevent sediment from entering the well. These wells were positioned one
 meter below the marsh surface, 0.6 meters above the soil surface, vented
 to the atmosphere, and only the section below the soil surface was
 perforated. Additionally, we installed concrete collars at the marsh
 surface around the wells to prevent preferential water flow down the well
 sides. These seven wells were placed along the original transect,
 perpendicular to the creek, with increasing distances (0 meters, 6 meters,
 12 meters, 18 meters, 24 meters, 36 meters, and 48 meters).
 We installed and monitored the wells from May 5 to June 30, 2019,
 and from April 6 to May 26, 1999. In 2019, we measured the absolute
 elevation of the top of each well using RTK-enabled static GPS
 measurements from Leica GNSS GS14 rover units and static measurements with
 an AX1202 GG base station unit to reference water levels to the NAVD88
 vertical datum. We measured reference water levels each time data was
 collected, which involved determining the distance from the top of the
 well to the water surface and converting it to elevation relative to the
 NAVD88 datum. To relate marsh elevation to water elevations, GPS surveys
 were conducted along the transect using a Leica GNSS GS14 rover unit. In
 1999, elevation control for the wells and water levels was similarly
 measured using survey-grade GPS. We compared changes in
 the marsh water table with significant potential hydrological and
 vegetation changes that have occurred over the past 20 years. We
 calculated the rates of change in monthly water levels at Battery, NY for
 the period from 1999 to 2019 using two different methods. We modeled
 changes over time in monthly highest water levels, mean high water (MHW),
 mean tide level (MTL), and mean low water (MLW) using an ordinary least
 squares regression model with ARIMA errors to account for the
 autoregressive structure of tide data. We removed the annual cycle first
 using a curve with a 1-year periodicity. The ARIMA errors model was fitted
 using the "auto.arima" function from the "forecast"
 package. We calculated the squared correlation of fitted values to actual
 values to produce a pseudo-r2. For comparison, we calculated trends using
 ordinary least squares regression for the 1999-2019 period, although
 it's important to note that the temporal autocorrelation likely
 results in underestimated uncertainty. We obtained
 vegetation maps from the HRNERR for 1997, 2005, 2014, and 2018 to help
 assess changes in the coverage of plant species over time, as these
 changes could impact evapotranspiration and water table patterns. A
 20-meter buffer zone was created around each well location, and the
 composition of vegetation within this buffer zone was quantified using
 QGIS version 3.30.2. While four time-points may not be sufficient for
 statistically identifying trends, we analyzed the changes
 observed. To put the measurement time periods in
 context and ensure that our selected seasons were not anomalous, we
 compared water levels in spring 1999 and 2019 relative to the astronomical
 cycles driving interannual sea level variability using data from the
 Battery tide gauge. We also compared spring high tide levels in 1999 and
 2019 with surrounding years. The main astronomical cycles thought to
 influence tides include the 18.6-year lunar nodal cycle and the 4.4-year
 subharmonic of the 8.85-year lunar perigee cycle. As our 1999 and 2019
 measurements were collected during slightly different time periods
 (April/May 1999 vs. May/June 2019), we also examined mean monthly water
 levels (1980-2022) from the NOAA Battery tidal gauge to identify potential
 artifacts. We obtained rainfall data from spring 1999 and 2019 from the
 nearest precipitation monitoring station (Westchester airport) to
 determine whether the measurements were made during an unusually wet or
 dry period. The sampling periods were 20 years apart, so they occurred at
 approximately the same point in the 18.6-year lunar nodal cycle.
 Pressure transducer data was processed using HOBOware Pro
 (Version 3.7.16, Onset Computer Corporation, Bourne, MA) with reference
 water levels collected in the field. The data were corrected for
 atmospheric pressure using the HOBOware barometric compensation assistant,
 using data from the Hudson River National Estuarine Research
 Reserve. Raw water elevation data from 1999 was
 analyzed in conjunction with the 2019 data. Water level data from 1999
 were converted from the NVGD29 to NAVD 88 datum using NOAA VDatum v4.0.1
 prior to analysis. Well seven's transducer experienced three brief
 malfunctions from May 30 to June 3, 2019, resulting in inaccurate
 elevation measurements for a total of 19.5 hours. These data were excluded
 from the analysis. In 1999, well seven also experienced malfunctions,
 which were corrected by Montalto into smoothed six-hour increments using
 average water elevation measurements and calculated error, calibrated
 using regression. No other well transducers appeared to have
 malfunctioned.
description: Climate and vegetation change in a coastal marsh: two snapshots of
 groundwater dynamics and tidal flooding at Piermont Marsh, NY spanning 20
 years We include water
 levels measured along a transect of groundwater wells in 1999 and 2019,
 statistical analyses of ground water data, tidal efficiency estimates,
 vegetation data from 1997, 2005, 2014, and 2018, measures of tide gauge
 data and sea level rise from the Battery, New York Harbor. We attach the
 following three groups of files: (1) Files related to data from Piermont
 Marsh, which includes water levels in wells, tide gauge data collected
 from the tidal channel, and vegetation data; (2) Files related to analysis
 of water levels at Piermont Marsh; (3) Files related to analysis of
 Battery tide gauge data, Battery tide predictions, and precipitation data
 ## Description of the data and file structure **(1) Files related to data
 from Piermont Marsh, which includes water levels in wells, tide gauge data
 collected from the tidal channel, and vegetation data**
 1999PiermontWaterlevels.csv 2019PiermontWaterLevels.csv channel_1999.xls
 channel_2019.xls water_level_elevations.csv Vegetation.xls
 1999PiermontWaterlevels.csv and 2019PiermontWaterLevels.csv - Water levels
 collected at Piermont marsh in groundwater wells, at 0-m, 6-m, 12-m, 18-m,
 24-m, 36-m, and 48-m from a tidal channel. The files contain three fields:
 daytime, well, and elevation. The daytime is the date and time the water
 level was collected, hours in Eastern Daylight Time -4GMT. The well number
 refers to its location relative to the tidal channel, with #1 referring to
 0-m, #2 referring to 6-m, #3 referring to 12-m, #4 referring to 18-m, #5
 referring to 24-m, #6 referring to 36-m, and #7 referring to 48-m. The
 elevation field refers to the water level in meters relative to the NAVD88
 datum. In 1999 water levels were collected 14 April 2019 - 26 May 2019. In
 2019, water levels were collected 5 May 2019 - 30 June 2019.
 channel_1999.xls - This file shows the elevation of water level in the
 channel. There is a field for date and time, in GMT -4, and water level in
 meters relative to NGVD29. channel_2019.xls - This file shows the
 elevation of water level in the channel. There is a field for Date, Time,
 in GMT -4, absolute pressure in in mbar, temperature in degrees C, and
 water level in meters relative to NAVD88. water_level_elevations.csv -
 This csv file includes five fields. The first is "year" or the
 year collected (1999 or 2019). The second is "well" numbered
 1-7. Well 1 is closest to the channel while 7 is the furthest from the
 channel. #1 referrs to 0-m from the channel, #2 referring to 6-m from the
 channel, #3 referring to 12-m from the channel, #4 referring to 18-m from
 the channel, #5 referring to 24-m from the channel, #6 referring to 36-m
 from the channel, and #7 referring to 48-m from the channel. The datetime
 field refers to the day and time the measure was made in day/month/year
 HH:MM AM/PM format. The next field is lunarcyle which refers to whether
 the measure was made during "spring" or "neap" tidal
 cycles. Spring was assigned to the tides the week of full or new moons,
 Neap was assigned to tides the week of the first and last quarter. The
 last is "elevation" and is the measure of water levels in meters
 relative to the NAVD88 datum. Vegetation.xls - This Excel file includes
 four sheets that each refer to a year of vegetation date - 1997, 2005,
 2014, and 2017. The first field is "well" which has a number 1
 through 7. The well number refers to its location relative to the tidal
 channel, with #1 referring to 0-m, #2 referring to 6-m, #3 referring to
 12-m, #4 referring to 18-m, #5 referring to 24-m, #6 referring to 36-m,
 and #7 referring to 48-m. There is a field for latitude (lat) and
 longitude (long), which refers to the location of the shape in UTM, in
 meters, in the 18N. Cover refers to the plant cover type, area is the area
 of the polygon in square meters. **(2) Files related to analysis of water
 levels at Piermont Marsh** Distancefromsurface.R MinNeap_MarshSurface.csv
 MaxNeap_MarshSurface.csv MinSpring_MarshSurface.csv
 MaxSpring_MarshSurface.csv PiermontEfficiencyRggplot.csv Tidalefficiency.R
 The R file Distancefromsurface.R includes calculations of mean and
 variance of water levels, and as well as production of relevant figures.
 MinNeap_MarshSurface.csv file has low tide minimum water levels during
 neap tides (weeks centered on the moons first and third quarter). It
 includes the following fields: distance, year, water_elevation,
 marsh_elevation, and distance_surface. The field distance, is distance
 from the tidal channel, in meters. The field year, refers to is the year
 collected (1999 or 2019). The field water_elevation, is the elevation of
 the water level at low tide, in meters relative to the NGVD88 datum. The
 field marsh_elevation refers to the height of the marsh at that location,
 in meters relative to the NGVD88 datum. The field distance_surface is the
 difference between the marsh elevation and the water elevation. Positive
 values are values below the marsh surface, while negative values are
 values above the marsh surface. MaxNeap_MarshSurface.csv file has high
 tide maximum water levels during neap tides (weeks centered on the moons
 first and third quarter). It includes the following fields: distance,
 year, water_elevation, marsh_elevation, and distance_surface. The field
 distance, is distance from the tidal channel, in meters. The field year,
 refers to is the year collected (1999 or 2019). The field water_elevation,
 is the elevation of the water level at high tide, in meters relative to
 the NGVD88 datum. The field marsh_elevation refers to the height of the
 marsh at that location, in meters relative to the NGVD88 datum. The field
 distance_surface is the difference between the marsh elevation and the
 water elevation. Positive values are values below the marsh surface, while
 negative values are values above the marsh surface.
 MinSpring_MarshSurface.csv file has low tide minimum water levels during
 spring tides (weeks centered on the new and full moon). It includes the
 following fields: distance, year, water_elevation, marsh_elevation, and
 distance_surface. The field distance, is distance from the tidal channel,
 in meters. The field year, refers to is the year collected (1999 or 2019).
 The field water_elevation, is the elevation of the water level at low
 tide, in meters relative to the NGVD88 datum. The field marsh_elevation
 refers to the height of the marsh at that location, in meters relative to
 the NGVD88 datum. The field distance_surface is the difference between the
 marsh elevation and the water elevation. Positive values are values below
 the marsh surface, while negative values are values above the marsh
 surface. MaxSpring_MarshSurface.csv file has high tide maximum water
 levels during spring tides (weeks centered on the new and full moon). It
 includes the following fields: distance, year, water_elevation,
 marsh_elevation, and distance_surface. The field distance, is distance
 from the tidal channel, in meters. The field year, refers to is the year
 collected (1999 or 2019). The field water_elevation, is the elevation of
 the water level at high tide, in meters relative to the NGVD88 datum. The
 field marsh_elevation refers to the height of the marsh at that location,
 in meters relative to the NGVD88 datum. The field distance_surface is the
 difference between the marsh elevation and the water elevation. Positive
 values are values below the marsh surface, while negative values are
 values above the marsh surface. PiermontEfficiencyRggplot.csv - file lists
 the well number (1-7), distance (a number 1-14, which gives a unique
 identifier to each combination of well and year), year, which was the year
 the data was collected. The last field is efficiency. This field refers to
 the ratio between the change in water level over the course of a tidal
 cycle in the well to the change in the water level over the course of the
 tidal cycle at the Battery tide gauge, NYC. Tidalefficiency.R - file that
 plots and calculates tidal efficiency during 1999 and 2019 at each well.
 **(3) Files related to analysis of Battery tide gauge data, Battery tide
 predictions, and precipitation data** MSL_time.R 3348871.csv 3348873.csv
 Battery.csv Bat_wls.csv monthly.csv sin2.csv predictions.csv tide_l.csv
 wls.csv MSL_time.R - This R code uses several data files to conduct
 analysis of change over time in water levels and monthly anomalies in
 precipitation and water levels. All necessary packages are described.
 3348871.csv and 3348873.csv - are weather data from Westchester County
 airport, station USW00094745 from 1997 to 2001 (3348873.csv) 2017 to 2022
 (3348871.csv). The field station lists the station. The field Name is the
 name of the station, Westchester County Airport. The date is the day data
 was collected. AWND refers to Average daily wind speed in miles per hour.
 PGTM refers to peak gust time (hours and minutes, i.e., HHMM). PRCP refers
 to precipitation in inches, TMAX refers to the maximum daily temperature,
 in degrees Fahrenheit. TMIN refers to the minimum daily temperature, in
 degrees Fahrenheit. WDF2 is the direction of fastest 2-minute wind in
 degrees. WDF5 is the direction of fastest 5-second wind in degrees. WSF2
 is the fastest 2-minute wind speed in miles per hour. WSF5 is the fastest
 5-second wind speed in miles per hour. Missing data is replaced with -999.
 Battery.csv - all high tide levels for 1997 through 2022. The two fields
 are level, referring to high tide water levels in meters relative to the
 NAVD88 datum. The second field is year. Bat_wls.csv is monthly tide levels
 from the Battery tide gauge, NY. The year field refers to year including
 fraction. Mean high water (MHW) refers to monthly mean high water relative
 to the NAVD88 datum in meters. Mean sea level (MSL) refers to monthly mean
 sea level relative to the NAVD88 datum in meters. Mean tide level (MTL)
 refers to monthly mean tide level relative to the NAVD88 datum in meters..
 Mean Low Water (MLW) refers to monthly mean low water relative to the
 NAVD88 datum in meters. monthly.csv - is mean high water and mean sea
 level from 1980-2022, by month. The field month refers to the month
 (January =1). MHW is monthly mean high water for all months, relative to
 the NAVD88 datum, and MSL is monthly mean sea level relative to the NAVD88
 datum. sin2.csv is the monthly mean sea level at the Battery tide gauge
 (1980-2022), with a 1 year rolling window median smooth added. There are
 three fields, month, MSL, and year. Month is the number of months elapsed
 since January 1961. MSL is the monthly mean sea level in meters, relative
 to the NAVD88 datum, with a one year smoothing function applied. Year
 refers to the observation month, expressed in years and the fraction of
 years so January 1980 would be 1980, while February 1980 is depicted as
 1980.083. predictions.csv - tide predictions for the Battery tide gauge,
 New York City. Fields are y, which stands for year, represented by year,
 including fractions representing months. High_p is the highest predicted
 tide of the month, in meters relative to the NAVD88 datum. MHW_p is the
 predicted mean high tide for the month relative to the NAVD88 datum. MLW_p
 is the predicted mean low tide for the month relative to the NAVD88 datum.
 MTL_p is the predicted mean tide level for the month relative to the
 NAVD88 datum. High_1 is the highest actual tide of the month, in meters
 relative to the NAVD88 datum. MHW_a is the actual mean high tide for the
 month relative to the NAVD88 datum. MLW_a is the actual mean low tide for
 the month relative to the NAVD88 datum. MTL_a is the actual mean tide
 level for the month relative to the NAVD88 datum. tide_l.csv is a file
 with the monthly mean high water (MHW_l), monthly mean tide level (MTL_l),
 and mean low water (MLW_l) for 1960 -2021. wls.csv is a file that has
 monthly water levels from 1999 to 2019, listing year (as a fraction, not
 just an integer for month), Highest, as the highest tide of the month in
 meters relative to the NAVD88 datum. MHW refers to the mean high water
 during the month in meters relative to the NAVD88 datum. MTL refers to the
 mean tidal level during the month in meters relative to the NAVD88 datum.
 MLW refers to the mean low water during the month in meters relative to
 the NAVD88 datum. <br> ## Sharing/Access information Data was
 derived from the following external sources: * Vegetation shapefiles for
 the Hudson River NERR for 1997, 2005, and 2014, were obtained through
 personal request to Sarah Fernald, *Reserve Manager and Research
 Coordinator.* Files should be available through the Reserve website,
 although the link is not functional at this time:
 * The 2018
 vegetation shapefiles were obtained from 
 under the heading, [Hudson River Estuary tidal
 wetlands](https://data.gis.ny.gov/datasets/ee2723393f894e929dbd6dbdc84770de_0/explore?location=41.308770%2C-73.842410%2C9.10). * We acknowledge the NYS DEC Hudson River Estuary Program, NYS DEC Hudson River National Estuarine Research Reserve, and Cornell Institute for Resource Information Sciences for collection and curation of the Hudson River NERR vegetation data. * Tide gauge data and tide predictions for the Battery, NY were obtained from NOAA tides and currents website: * Precipitation data was obtained from the National Centers for Environmental Information, NOAA: . The station for which data was obtained was the Westchester County airport, station USW00094745. ## Code/Software We provide three R files, which we ran using R version 4.3.1 (2023-06-16), in R Studio 2022.02.1, Build 461. All required packages are described in the .R files. Distancefromsurface.R - This R code utilizes four data files that include low tides during spring tides, low tides during neap tides, high tides during spring tides, and high tides during neap files to compare average and variance in low and high tide water levels during 1999 and 2019 relative to the marsh surface and relative to the NAVD88 datum. Code is also included to produce plots. Tidalefficiency.R - file that plots and calculates tidal efficiency during 1999 and 2019 at each well. MSL_time.R - This R code uses several data files to conduct analysis of change over time in water levels and monthly anomalies in precipitation and water levels.