Bacterial and Phytoplankton Dynamics along a Trophic Gradient in a Shallow Temperate Estuary

The Effects of System-Level Nutrient Enrichment on Bacterioplankton Production in a Tidally-Influenced Estuary**

“…Four estuaries emerged where the relationship between BP and CHLA was relatively strong (Figure 4): Indus River Delta ), Menai Strait (BLIGHT et al, 1995, Urdaibai estuary (REVILLA et al, 2000), and North Inlet-Winyah Bay NERRS (present study). These systems were generally more saline (i.e., 22-37) and represent a broad geographic range and estuary types.…”

“…Paired measures of BP and CHLA from Monie Bay had a similar distribution to that of other estuarine systems but no significant relationship (p Յ 0.6, n ϭ 159). Four systems emerged from the literature and field data that exhibited highly significant and relatively strong covariation of BP and CHLA (Figure 4), including Indus River Delta , Urdaibai estuary (REVILLA et al, 2000), Menai Strait (BLIGHT et al, 1995), and North Inlet (present study).…”

“…However, covariation of BP and CHLA may also occur if both bacterioplankton metabolism and phytoplankton biomass are simultaneously yet independently regulated by an external factor, such as inorganic nutrient availability (e.g., COVENEY and WETZEL, 1995;SMITH and KEMP, 2003;VREDE et al, 1999). Under such circumstances, nutrients subsidize algal production while bacterioplankton combine nutrients with allochthonous (i.e., nonalgal) sources of organic matter to fuel growth, evidence of which was observed in the studies discussed earlier (i.e., REVILLA et al, 2000). The independent but proportional effect of nutrients on BP and CHLA may explain why we failed to observe a relationship between dissolved nutrient concentrations and BP : CHLA ratios, because if BP and CHLA increase proportionally along a eutrophication or nutrient gradient, BP : CHLA will remain relatively unchanged.…”

“…Such direct coupling did not appear to drive the covariation of BP and CHLA in other systems, where the two parameters exhibited strong coherence. Urdaibai estuary is a turbid, nutrient-enriched environment in northern Spain where bacterioplankton carbon demand is subsidized by anthropogenic inputs of organic wastes (REVILLA et al, 2000). Covariation of BP and CHLA in this system most likely results from the absence of nutrient limitation for algal and bacterial growth, combined with subsidy of the latter by inputs of allochthonous organic matter.…”

“…The temporal and spatial variability of these systems is such that environmental conditions for even a single category of estuary (e.g., drowned river valleys) may vary tremendously both within and among such systems (DAY et al, 1989). In addition, the primary factors regulating plankton community activity and abundance are highly variable among estuarine systems and include anthropogenic nutrient inputs (REVILLA et al, 2000), light availability (HARDING, MEESON, and FISHER, 1986), salinity (PRADEEP RAM, NAIR, and CHANDRAMOHAN, 2003), season, temperature, and organic matter source and quality (APPLE, DEL GIORGIO, and KEMP, 2006;LOMAS et al, 2002;RAYMOND and BAUER, 2000). As a result, identifying representative estuarine systems is challenging, since the primacy of any one parameter in driving the physical and biological variability is, in itself, highly variable among systems.…”