| Summary |
A transect from the Atlantic Ocean to Bogue Sound was established in November of 1974 in the Roosevelt Natural Area at Salter Path, North Carolina. Stations, designated by their distance in meters from the ocean, were studied from 8 December 1974 to 2 July 1976. Chloride (Cl), calcium (Ca), and magnesium (Mg) were monitored in bulk precipitation, throughfall, humus leachate, soil, standing water, and ground water. Quantities of water in gross rainfall and throughfall were determined as v/as the soil moisture. Vegetation at stations across the island was described in terms of canopy species composition and diversity. Quercus laurifolia and virginiana dominated the forest canopy in non-innundated areas, while Fraxinus tomentosa dominated the canopies at swale stations. Canopy height was inversely correlated with inputs of chloride (r = -0.87, P = 0.05). Atmospheric inputs of rain and dissolved Cl, Ca, and Mg into the fores and adjacent shrub thicket were collected by placing rain gages at the canopy surface over two study years (8 December 1974 to 6 December 1975 and 26 June 1975 to 7 June 1976). The gages were located at canopy level at nine stations along the transect and at one site in the Juncus-Distichlis salt marsh that borders the forest on the sound side. Samples were analyzed for chloride over both study years and for calcium and magnesium over the second study year. Inputs of chloride (g-m⁻²yr⁻¹) over the first year ranged from 107 (at Station 57) to 16.5 (Station 325). Stations 680, 848, and 879 showed increasing chloride inputs resulting from salt spray from Bogue Sound. For the second year maximum atmospheric inputs were recorded at Station 124. These inputs (g-m⁻²yr⁻¹) ) were Cl = 104, Ca = 3.07, and Mg = 6.67. Station 396 had the lowest annual inputs, these were; Cl = 20.0, Ca = 1.38, and Mg = 0.99. It was possible to describe the patterns of salt spray inputs across the island from ocean to sound by linear regression equations. Regression analysis of atmospheric inputs as a function of a topographical factor (calculated from the distance from the ocean, the distance from the sound, and elevation above mean sea level) resulted in equations for the prediction of atmospheric mineral inputs at any site along the transect where the topography is known. The equations were found to be: (1) Cl, Y= 21.9 X - 5.48, (2) Ca, Y= 0.40 X + 0.98, and (3) Mg, Y= 1.11 X - 0.26 (where Y is the atmospheric inputs in g-m⁻²yr⁻¹ and X is the topographical factor). This method of prediction also yielded good results for chloride data from the first year (r= 0.80, P= 0.05) and for data on topography and salt spray inputs gathered from a previously published study by another author. The patterns of Cl and Mg in throughfall paralleled those in bulk precipitation. Both Ca and Mg were enriched in throughfall relative to bulk precipitation because of additional ions leaching from the foliage and the washing off of aerosols impacted on foliage. Soil along the transect was found to contain low quantities of water soluble minerals either in the upper 30 cm or at the water table depth. The maximum annual means of soluble Cl and Mg in the upper 30 cm of soil were found at Station 57 (Cl= 8.24 and Mg= 3.03 g-m⁻²). The lowest quantities of Cl and Mg were found in soils from Station 396 (Cl= 5.09 and Mg= 0.09 g-m⁻²). For Ca there was little variation among the soils of the four stations monitored. The range of Ca for these soils was 0.57 to 0.29 g-m⁻². To develop a working model of mineral cycles on a barrier island, intersystem transfers and storages must be coupled with the gradient of atmospheric inputs across the island. Data presented here constitutes an important contribution toward the development of Cl, Ca, and Mg budgets for Bogue Bank. Also prediction of atmospheric inputs from a calculated topography factor provides a method for estimating the input gradients needed to develop models for Cl, Ca, and Mg on Bogue Bank. |
