When barley straw and deciduous leaf litter decompose aerobically in water,
inhibitors are released that suppress the growth of nuisance algae. Barley
straw has been widely used for algal control in small, shallow lakes and w
e review the advantages and disadvantages of the method. It is particularly
effective at promoting the switch from algal to macrophyte domination. Des
pite its cheapness and apparent safety in the short term, however, the use
of barley straw requires considerable management effort and the long-term e
cological safety of such un-natural litter inputs is unkown. We therefore r
ecommend it to lake managers primarily as a short-term measure. Deciduous l
eaf litter from a range of woody species can suppress the growth of Chlorel
la and Microcystis very effectively in laboratory bioassays and, in field t
rials with medium-sized ponds, the addition of leaf litter produced signifi
cant inhibition of the filamentous alga Cladophora glomerata. We followed t
he development of algal inhibitory activity over 2.5 years with freshly fal
len oak leaves placed in a large tank of aerated water and using Chlorella
as the test species. Two periods of inhibitor release were identified: 4-90
days (early phase) when soluble, relatively stable inhibitors were present
in tank liquor, probably generated from oxidized tannins; and 120-900+ day
s (late phase) when inhibitors were relatively unstable in solution and wer
e associated primarily with fine particulate organic matter (FPOM). Late ph
ase inhibitors may, as suggested for barley straw, be generated during the
oxidative breakdown of lignin. The prolonged and powerful anti-algal proper
ties of these natual litter inputs offer possibilities for low-effort, sust
ainable management of lakes and catchments so as to reduce the problem exce
ssive algal growth.