Calibration of a Bio-optical Model in the North River, North Carolina (Albemarle–Pamlico Sound): A Tool to Evaluate Water Quality Impacts on Seagrasses

Seagrasses are typically light limited in many turbid estuarine systems. Light attenuation is due to water and three optically active constituents (OACs): nonalgal particulates, phytoplankton, and colored dissolved organic matter (CDOM). Using radiative transfer modeling, the inherent optical properties (IOPs) of these three OACs were linked to the light attenuation coefficient, K _PAR, which was measured in North River, North Carolina, by profiles of photosynthetically active radiation (PAR). Seagrasses in the southern portion of Albemarle-Pamlico Estuarine System (APES), the second largest estuary in the USA, were found to be light limited at depths ranging from 0.87 to 2 m. This corresponds to a range of K _PAR from 0.54 to 2.76 m^?1 measured during a 24-month monitoring program. Turbidity ranged from 2.20 to 35.55 NTU, chlorophyll a from 1.56 to 15.35 mg m^?3, and CDOM absorption at 440 nm from 0.319 to 3.554 m^?1. The IOP and water quality data were used to calibrate an existing bio-optical model, which predicted a maximum depth for seagrasses of 1.7 m using annual mean water quality values and a minimum light requirement of 22% surface PAR. The utility of this modeling approach for the management of seagrasses in the APES lies in the identification of which water quality component is most important in driving light attenuation and limiting seagrass depth distribution. The calibrated bio-optical model now enables researchers and managers alike to set water quality targets to achieve desired water column light requirement goals that can be used to set criteria for seagrass habitat protection in North Carolina.     

Comment on: “Enriched mantle – Dupal signature in the genesis of the Jurassic Ferrar tholeiites from Prince Albert Mountains (Victoria Land, Antarctica)” by Antonini P. et al. (Contributions to Mineralogy and Petrology 136, 1–19; 1999)

18 O values, the magmas retain initial ⁸⁷Sr/⁸⁶Sr Compositions of greater than 0.709 (e.g. Hoefs et al. 1980). Consistent with this is the lack of a radiogenic Os isotope signature in these rocks (e.g. Molzahn et al. 1996) as would be expected with assimilation of continental crust. Comments here are not concerned with the AFC calculations employed to describe the variations within the suite of samples from the Prince Albert mountains studied by Antonini et al., but rather, the extrapolation of these to more primitive compositions. Antonini et al. have revived the possibility that the unusual chemical features of the least evolved low Ti continental flood basalts of the Ferrar Province reflect a crustal-level interplay between mantle-derived magmas and the continental crust. It is argued here that they have not demonstrated their claim. Received: 7 October 1999 / Accepted: 25 January 2000     

Reply to ‘Comment on: “Establishing the Late Pleistocene-Holocene sedimentation boundary in the southern North Sea using OSL dating of shallow continental shelf sediments” by L. Alappat,A. Vink,S. Tsukamoto,M. Frechen,Proceedings of the Geologists’ Association 121 (2010), 43–54’ by B. Mauz

The major concerns in the correspondence of Mauz (2012) was the correction applied for the calculation of cosmic dose in response of changing sea level in the past and statistical parameters used as well as the selection of MAM. A better approach is discussed in this note for the calculation of cosmic dose over a variable time span of rising sea level with the help of established sea level curves in the area. The selection of MAM-3 for the estimation of final De's are discussed in the article. The comments by Mauz (2012) have been helpful in rectifying some confusions that might have arisen in the original article of Alappat et al. (2010). However, some comments were merely speculative in nature and made by ignoring the statements that have been clearly mentioned in the article. After addressing various concerns of Mauz (2012), the results show that the variation in the final age due to this is small and within the uncertainty for all the samples.