In comparison to rivers and estuaries of the world, the tidal-freshwater Hudson, depending on the location, was fairly eutrophic prior to the invasion of the zebra mussel in 1992. That is, mean growing season chlorophyll-a at Kingston, New York, was higher than more than 75 percent of the rivers and estuaries for which we have data. Similarly, the Kingston region had high chlorophyll in comparison to downriver sites within the Hudson. Following 1992, (post-) chlorophyll-a in the mid Hudson would be considered moderately low in comparison to other river or estuarine systems (Fig. 9.9A).
As we pointed out, GPP is rarely measured in most systems, making comparison limited. However, we can compare our estimates of phytoplankton GPP to estimates of GPP made on the saline part of the Hudson River Estuary, many of which are reviewed in Chapter 10 andSwaney et al. (1999). GPP for the mid 1990s is about 850 g C m-2 y-1 in the saline part of the estuary and 450 g C m-2 y-1 for the oligohaline section. Both estimates are considerably higher than we estimate for the freshwater portion of the river of 330 g C m-2 y-1 for the pre-zebra mussel period and 82 gCm-2 y-1 post zebra mussel. On the other hand, the estimates reported by Howarth et al. (Chapter 10) for the mid 1990s are roughly 2 to 4 times higher than prior estimates from the 1970s for the saline and mesohaline sections, respectively. So, prior to the zebra mussel, GPP in the tidal-freshwater portion of the estuary was somewhat lower than for the oligohaline region and less than half that for the saline portion. Following the invasion, GPP in the tidal freshwater was only about 25 percent of that in the oligohaline region and roughly one-tenth the estimates for the saline portion.
Figure 9.9. Phytoplankton biomass (A) and primary production (B) in comparison to other rivers (filled circles) and estuaries (open circles). Each point is for a different riverine or estuarine system, and the systems are ordered by chlorophyll values from low to high. Biomass is mean chlorophyll-a for the growing season. For the tidal-freshwater Hudson this is given for both prior to the zebra mussel invasion ("pre-") and following it ("post-"). Several other sites for the saline estuary are also shown. These are NYH - New York Harbor (Malone, 1975; Malone, 1977), and HW-HaverstrawBay andVB-Verrazano Bridge (both from G. Taylor, personal communication) and are data from the mid-1990s.
For primary production values are net daytime photic zone production for the mid Hudson. For other systems we assumed the "NPP" was equivalent to our NDPZP. Values are expressed as daily means for the entire year. Non Hudson data are from Cadee and Hege-man, 1974; Cloern, 1984; Cloern, et al., 1985; Cole and Cloern, 1984; Bonnetto, 1983; Frey et al., 1984; Cadee, 1986; Ertl, 1985; Fisher et al., 1982; Flint et al., 1986; Gopinathan et al., 1984;Harding et al., 1986; Levasseur et al., 1984; Pennock and Sharp, 1986; Scott, 1978; Sinada and Karim, 1984; Shehata and Bader, 1985; Stockner and Cliff, 1979; Turner et al., 1979; Baker and Baker, 1979; Flemer, 1970; Furnas et al., 1976; Gilmartin, 1964; Haines and Dunstant, 1975; Keller, 1988; Kuparinen, 1987; Randall and Day, 1987.
In order to compare planktonic primary production in the tidal-freshwater Hudson more broadly to the saline parts of the estuary and New York Harbor, as well as to other estuaries and rivers, we need to revert to our estimate of NDPZP, which is akin to what most researchers report as "NPP."
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