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b. on Staten Island organic soil that will be converted to wetlands,so and they will be representative of baseline subsidence c. In the Delta conditions. Implementing rice will stop subsidence H S2 e Explanation Soil physical and climatic factors influence subsidence rates H S3 • UIly cI, a Ta 9 • Pevbus Twer Lo,atiorr Subsidence rates vary spatially in the Delta H S4 a EranaomMers EUEy Covanarce Foo�p'�ni o sumo s�oaa —arana •••••••.Eiavaoon fa) Step 5:Current data need:metrics Ea somner Metric:Land Surface Elevation Rationale:Land surface elevation is a direct indicator of subsidence.Surface elevation may fluctuate with water level fluctuation beneath the highly organic soils,but microbial oxidation of organic matter leads to the overall sinking of the island floor or inelastic subsidence.Organic material is broken down producing CO2 emissions and reducing the actual mass of the soil.Surface elevations are expected to decline while the land is used for corn production.Rice cultivation is expected to halt subsidence and permanent wetlands are expected to reverse subsidence due to aerobic conditions on flooded fields. The actual change in surface elevation as a result of organic matter oxidation or accretion is critical for e / quantifying the rate at which these processes occur. Method:Land surface elevation will be measured following the methods described by Deverel and o o z o 1 08 1.2 Is a<s Rojstaczar(1996)and in Deverel et al.(2016).An extensometer will be used to measure land surface Figure 4:Locations of extensometer and water quality measurements elevation changes Hydro Focus will install extensometers to monitor continuous variations in land surface elevations with a linear variable differential transformer(GHSI 750 LVDT).Land-surface elevation variations will be measured relative to the extensometer structure which will be anchored below the organic soil.Three metal pipes will be driven to refusal into the mineral layer below the peat.Three lengths of angle-iron will be welded onto the pipes and to each other to form a level horizontal Metric:Groundwater Elevations equilateral triangle.A Macro Sensors HSI 750 LVDT will be fastened vertically to one of the triangle sides, Rationale:Soils with high organic content demonstrate some degree of elasticity from fluctuating with its piston arm resting on a X-inch-thick aluminum plate on the ground. water levels.Ground water levels must be known to account for these shifts and to accurately assess subsidence caused exclusively by soil oxidation.Groundwater levels are influenced by the hydraulic Timing: Land surface elevation may be variable during the year due to groundwater fluctuations and gradient from adjacent rivers.drainage and water applied to the land surface as rain or irrigation.The the elasticity of the organic soils.The rate of organic matter oxidation is also dependent on the amount depth to groundwater on subsided Delta island is controlled by a network of drainage ditches feeding to of organic matter in the soil,degree of saturation(oxygen content),and temperature.Crop growing drainage pump stations that discharge drainage to the Delta channels.The depth to groundwater is also cycles,like those with corn and rice,may also influence subsidence.Continuous measurements are an important factor in determining the depth of the organic soil where oxidation will occur(Deverel et critical to account for temporal variability in all the factors when determining annual inelastic al.,2016).Saturated organic soils are not expected to contribute to subsidence due to the slow subsidence rates.A data logger will record LVDT measurements every 15 minutes.The elevation of the decomposition rates of the anaerobic environment. extensometer and ground surface will be measured by GPS at the start of monitoring and once each month.Manual measurements of the distance between the fixed structure.and the land surface will be Method:A monitoring well will be built at each extensometer location.Water-depth transducers will taken at least once per month for comparison with the logged data using a caliper.Measurements will be deployed in each well to measure the height of water above the instrument.The transducers(In-situ continue for 12 months. Leve Trolls)will record the depth ofwater every 15 minutes and store the data on the local device memory.The well elevation will be measured via GPS at the start of monitoring.Manual water level Location: Land surface elevation will be measured at two locations in southern Staten.One measurements will be made with an electronic sounding device for comparison with and verification of extensometer will be placed in the cornfield inside the eddy covariance footprint,the other will be the logged data. placed in a corn field in southeast Staten,where the wetlands will be implemented(Figure 4).The two proposed extensometer locations are located in areas of the same land use and the same type of highly