A study of the nitrogen content of dune soils, with particular reference to the effects produced by the sea-buckthorn, Hippophae rhamnoides L.

Mason, Alan Leonard Frederick (1986). A study of the nitrogen content of dune soils, with particular reference to the effects produced by the sea-buckthorn, Hippophae rhamnoides L. BPhil thesis The Open University.

DOI: https://doi.org/10.21954/ou.ro.0000f93a

Abstract

The history of research into the chemistry of dune soils is reviewed, with particular reference to the presence of nitrogen compounds, and also the effects created by the nitrogen-fixing shrub, sea-buckthorn (Hippophaë rhamnoides, L.).

Problems associated with the colonization of sand dunes by Hippophaë were investigated in the main study, involving soil sampling at selected sites between December 1980 and November 1981 on the Norfolk coast near Hunstanton. Hippophaë scrub of different ages was chosen, and control sites were left undisturbed. At experimental sites thick polythene sheeting was buried below the surface sand to prevent the downward percolation of solubles.

Subsidiary investigations were made of other coastal sites in Britain, some with, and some without, Hippophaë colonies. The soil samples were analysed principally for nitrate ion, but also for ammonium, phosphate, and carbonate ions.

The investigations revealed that nitrate levels in dune soil are proportional to the age of the Hippophaë scrub. A seasonal variation in nitrate levels was observed, with peaks in April and September. A model nitrogen economy was proposed to account for this.

Statistical tests revealed no significant differences between control and experimental sites suggesting that nitrate is derived principally from Hippophaë rather than the leaf litter or animal products, probably by routine disintegration of the root nodules.

The subsidiary sites lacking Hippophaë colonies had no detectable nitrate, or very low levels (< 0.5 ppm) even when heather scrub (Studland Heath, Dorset) or hawthorn scrub (Daymer Bay, Cornwall) was present. This confirms the view that the nitrate detected at Hunstanton came from the Hippophaë scrub.

Where Hippophaë was prolific (Gibraltar Point, Lincolnshire) the levels of nitrate detected were higher than at Hunstanton, even in the uncolonized sand of the beach, due possibly to the circulation of nitrates within the ground water of the dune system.