The dynamics of submerged macrophytes were studied in a large and shallow near-pristine lake in New South Wales, Australia. The objectives were to investigate the seasonal dynamics in biomass of Chara fibrosa, Nitella hyalina and Najas marina both in time and space, and to characterise the underlying relationship between the plant biomass and both the gyttja and water depths. Charophytes were most densely grown in the north-east bays of the lake compared to the north-west bays. Average biomass of Chara fibrosa was highest at the north-east bays of this lake (e.g. 210 g d.w m −2 ) followed by north-west bays (e.g. 148 g d.w/m 2 ), South-west bays (e.g. 60 g d.w/m 2 ) and lastly central deep area of the lake (e.g. 31 g d./m 2 ). A similar trend was displayed by Nitella hyalina biomass where at the north-east bays the biomass was the highest (e.g. 167 g d.w m −2 ) followed by north-west bays (e.g. 128 g d.w/m 2 ), south-west bays (e.g. 38 g d.w/m 2 ) and central deep area of the lake (e.g. 23 g d.w/m 2 ). During the summer season the maximum total biomass of charophytes at Corrigans bay was recorded (e.g. 300 g d.w/m 2 ), mostly being dominated by Nitella hyalina. Total biomass of charophyte was reduced during the winter season (e.g. 50 g d.w m −2 ). Najas marina biomass remained low both in time and space except in May at Bibby harbour and Shelly beach where its biomass peaked (e.g. 276 and 175 g d.w m −2 respectively). Gyttja depth showed a positive relationship with total charophyte biomass (r 2 = 0.70; p < 0.01) and it seemed to favour the growth of charophytes at the expense of other submerged macrophytes, e.g. Myriophyllum sp. and Vallisneria sp. Water depth displayed a negative relationship with total charophyte biomass (r 2 = −0.94; p < 0.01). Both Chara fibrosa and Nitella hyalina correlated positively with gyttja depth (r 2 Chara-gyttja) = 0.69, r 2 Nitella-gytja) = 0.65; p < 0.01) and negatively with water depth (r 2 Chara-depth = −0.94, r 2 Nitella-depth = −0.93; p < 0.01). Najas marina correlated positively only with water depth (r 2 = 0.67, p < 0.01).

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