Nutrient Reference Conditions in New Jersey Lakes Based on Analysis of Sediment Cores: Research Project Summary



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Trenton, N.J. : New Jersey Department of Environmental Protection, Division of Science, Research and Environmental Health


This project was conducted to more accurately quantify reference water-quality conditions in New Jersey (NJ) lakes. An accurate quantification of reference conditions is required to support the development of numeric nutrient and other biological criteria needed in setting realistic targets for protection and restoration plans. This project provided data on historic lake nutrient conditions, including undisturbed natural conditions characteristic of the pre-European settlement period. The project had two main objectives: 1) quantify reference (pre-European settlement) trophic conditions and 2) assess the amount of change induced by anthropogenic activities on lake nutrient concentrations using diatom-based inference models. To reach these objectives, sediment cores have been collected and analyzed for diatom species present in the top core interval (present-day conditions) and bottom core interval (past lake conditions, could represent pre – or post-European). The field crew aimed to obtain 1-m long cores, which based on scientific literature should reach preEuropean time in lakes from the northeastern USA. Two steps were used to determine if core bottom intervals represented the pre- European time period for each specific site: 1) pollen composition and relative abundance of Ambrosia pollen; and 2) radioisotope dating. Pb-210 radio isotope dates were used to determine if the core bottom intervals were older than ~100 years, which is the oldest age that Pb-210 can provide. Results suggest the core bottom sediments in most of the lakes were deposited at least 100 year ago; these core bottoms, may or may not reach preEuropean time period. The Ambrosia pollen is a well-known chronomarker for the European settlement. Since settlement was marked by extensive forest clearing and replacement of clear-cut areas by Ambrosia plants, pollen counts of Ambrosia were used to determine if the bottom core was deposited before or after the European arrival. Bottom sediment samples from a few cores had Ambrosia pollen as high as 36 percent suggesting that they did not represent a time period prior to European settlement, while other bottom intervals had pollen assemblages atypical from today, without invasive species and with very low concentrations of Ambrosia pollen suggesting they represent the pre-European settlement time period . A total of 122 diatom samples were analyzed in top and bottom core intervals. Overall, top core sediment samples (representing current conditions) are rich in Fragilaria crotonensis, Asterionella formosa and Fragilaria capucina. These species are indicators of eutrophic conditions. Core bottom sediment samples are dominated by Cyclotella michiginana, a species indicative of low total phosphorus concentrations. The average diatom-inferred total-phosphorus concentration from all surface samples is 48 µg/L. The historic average diatom-inferred total-phosphorus concentration determined from all core bottom samples is 24 µg/L, just less than half of the current water quality standard for NJ. Total phosphorus estimates in bottom sediment samples were typically higher in impoundments than from natural lakes.


Prepared by Mihaela Enache, Ph.D.


New Jersey, Lakes - New Jersey