Thursday, July 26, 2012

Hydrophytic vegetation of the San Joaquin Delta

With the revival of quasi-dormant debate over the Peripheral Canal/Tunnel,  I point out our poor understanding of Delta flora and vegetation in relation to salinity gradients.  Marsh salinity in the Delta region is suspected to have undergone a strong, directional increase associated with anthropogenic hydrologic modification.  I have not yet found a comprehensive analysis of existing vegetation salinity gradient relationships, and consequently wonder if any such study has been undertaken.  Predicting future vectors of marsh ecosystem change, and any but feeble hope for restoration, needs to account for pre-settlement flora and vegetation conditions in the Delta.

On July 17, 1896 Willis Jepson collected yellow pond lily (Nuphar polysepala) at Stockton.  Nuphar polysepala is a scattered, important member of the hydrophytic flora of Sierran lakes, mainly at about 7000 ft.  Nuphar does occur at low elevations, such as in Marin County, and other coastal lakes.  The occurrence of N. polysepala in the deltaic Great Valley is significant because this taxon is a indicator of water salinity: it is salt intolerant (1). 

Nuphar polysepala was still extant near Stockton at least until the early 1970s.  In the mid-1960s, it was still present in Pixley Slough.  In the 1970s, it was present near Snodgrass Slough near Locke, although this latter site was not recorded by Bowcutt (2).   Very probably, if salt water intrusion has taken its toll on the Delta hydrophyte flora, Nuphar would now be extirpated.  Is it? 

Several other hydrophytes are known from >60-100 yr old historical records in the Delta: Carex comosa near Holt in 1928, Meneyanthes trifoliata (3), Potamogeton nodosus in 1928, P. zosteriformis in 1949 etc etc.  Lycopus americanus, another non-saline hydrophyte, is apparently still present as of 2002. 

These non-saline hydrophytes are indicators of delta water quality and their local distribution, and their placement in a data-based gradient analysis of Delta marsh vegetation is needed.  

I poist that saline intolerant hydrophytes have been eliminated from much of the Delta region associated with the inland intrusion of brackish or saline waters.  If these non-halophytic halophytes persist today, their communities become a model for restoration.  Where might this persistent, original hydrophytic vegetation remnants be ?

1.  Padget, D. et al. 1999. American Journal of Botany 86(9): 1316–1324.
2.  Bowcutt, F.  1996. Madrono Vol. 43, no. 3, pp. 417-431.
3.  Mason, H.  1957. Flora of the Marshes of California. UC Press

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