B. Papp szerk.: Studia Botanica Hungarica 35. 2004 (Budapest, 2004)

Gönczöl, János; Révay, Ágnes: Aquatic Hyphomycetes in two streams differing in discharge and distribution of leaf litter

The relatively high conidial concentration (27,992 conidia L

') at site 1 decreased to 10,933 L-1 at site 2, while the discharge (0.8 L s~' at site 1) increased more than tenfold (8.8 L s

_1 at site 2) in the Deszkametsző. On the contrary in the Bagolybükk, which is a relatively fast flowing stream, with a more or less straight streambed, the number of conidia increased downstream, from 2,769 Lr

1 at site 1 to 6,660 Lr

1 at site 2, while discharge decreased by almost 50% between the two sites. An opposite trend in the downstream changes in conidial concentrations was also observed in two other second-order tributaries of the Morgó stream system in a former study (GÖNCZÖL and RÉVAY 2003) but no discharge was measured in these tributaries. The conidial concentration and discharge between the upper and lower sites in the Csömöle stream, a previously studied tributary, changed similarly to those in Deszkametsző. The conidial numbers decreased downstream from 23,644 L~' to 4,224 Lr

1 between the two sites of the Csömöle stream, while the discharge increased by about 50% (1.0 L s"

1 to 2.1 L s

1

) (GÖNCZÖL and RÉVAY 1999, and unpubl. obs.). The upper reaches of both streams are very similar to each other in some characteristics, i.e. slowly flowing shallow water, low discharge and meandering streambed loosely filled with a continuous layer of leaf litter. We concluded that some 20,000 or more conidia Lr

1 in November and December seems to be a general pattern in the upper reaches of these slowly flowing, small streams. This may be mainly due to the very effective retentive capability of these streams. The amount of litter and discharge are evidently crucial factors to control conidial concentration in a given reach of a stream (BÄRLOCHER 1992a). Our results obtained for five second-order tributaries in the Morgó stream system suggest that discharge, the amount and structure of litter are important factors to determine conidial concentrations in headwater streams. Relatively few data are found in the literature about the effect of discharge and changes in type and quantity of allochthonous litter on conidial concentration in streams. SHEARER and WEBSTER (1985a) studied the longitudinal variation in aquatic hyphomycetes at three sites along the River Teign (England). They found that conidial numbers increased in a downstream direction. The amount of allochthonous material was probably an important factor in determining numbers of conidia as it was always lesser at the most upstream site than the two lower sites. In a study of aquatic hyphomycetes at two sites of the Catamaran Brook (Canada) a significant downstream decrease in conidial numbers was found by BÄRLOCHER (2000). He concluded that the decline of conidial numbers might be due to dilution since water discharge increased considerably between the two sites. SUBERKROPP (1997) found that spore concentrations in a small woodland stream, Walker Branch (Tennessee, USA) were significantly correlated with the amount of leaf material present. Spore concentration one to four spores ml-1