Spectral Characteristics of Inter-tidal mud flats in impoundments at low and high tide


Norman Yao and Francisco Artigas, Meadowlands Environmental Research Institute



Algae and other plant and animal life are intricate aspects of the mud ecosystems of tidal wetlands. Spectroradiometers capture the light reflectance of a target in narrow bands covering the visible, near-infrared and infrared portions of the spectrum. The premise of this study is that these electro-magnetic impulses can be linked to biophysical processes taking place in the mud ecosystem. Algae mat biophysical processes are affected mainly by hydrology, runoff, culvert arrangement and impoundment size.  Understanding the spectral responses and associated biophysical processes of mudflats provides the key to mapping these processes using hyper-spectral images from sensors mounted to fixed wing aircraft and orbiting satellites. The specific objectives of this study were two fold. First, determine the effects of mud elevation, impoundment size, and culvert arrangement on the spectral response of algae mats.  Second, determine the effects of optically active compounds in the water column on the spectral response of the mud flats at high tide. Reflectance spectra were collected from samples along transects in three different impoundments. The impoundments have different dimensions, depths and distinct culvert connectivity arrangements. In each impoundment, the sampled transects ran the length of the inter-tidal zone from the high tide mark to the low tide mark. Spectral measurements along transects were made with a field spectroradiometer which captured light reflectance between 350 and 2500 nm. Spectral measurements were taken along all three transects at low and high tide. During low tide, samples of exposed mud surfaces were collected and examined for invertebrates and algae diversity. During high tide, a surface water sample was collected at each sampling point and the concentrations of the optically active compounds were determined in the lab. Spectral curves from the exposed mud flats were compared among impoundments and between elevations along specific transects. The presentation will show the relationship between mud flat elevation, impoundment size and connectivity on the spectral response of algae mats. The study will also present findings regarding the effect of high tide on the spectra of inter-tidal mud surfaces.