Shallow Subtropical Lake Research Articles

Forms and distribution of inorganic phosphorus in sediments of two shallow eutrophic lakes in Florida

Phosphorus (P) reactivity and bioavailability in lake sediments may be determined by different forms of P and their distribution. Reactive and nonreactive P pools in two shallow subtropical lake sediments (Lake Apopka and Lake Okeechobee) were determined by sequential chemical extraction using 1 M NH4Cl (pH 7.0), 0.1 M NaOH, and 0.5 M HCl, reportedly representing loosely-bound P, Fe- and Al-bound P, and Ca- and Mg-bound P respectively. The sequential P fractionation was tested using pure P compounds and selected P minerals. The scheme effectively separated Fe- and Al-P from Ca-P fractions in an FePO4-AlPO4-Ca3(PO4)2 mixture. Readily available P, defined as the sum of water-soluble P and NH4Cl-extractable P, in the unconsolidated gyttja (UCG) layer (surface 0–30 cm) of Lake Apopka sediments accounted for 10.1 to 23.7% of total P (TP). This sediment P fraction constitutes a large reservoir which may act as a source of P to the overlying water. In subsurface marl layers (134–148 cm depth) of Lake Apopka, NH4Cl-P constituted <I% of TP whereas Ca-Mg-bound P and highly resistant P (residual P) accounted for 35 and 64% of TP respectively. Results suggest that 1 M NH4Cl (pH 7.0) and 0.5 M HCl, reported to dissolve carbonate-bound P and Ca-Mg-bound P, respectively, may not be extracting distinct pools of P. Lake Okeechobee mud sediments had low concentrations of readily available P (2% of TP) and were dominated by Ca-Mg-bound P (HCl-P≥58% of TP). Sediments in the littoral and peat areas of Lake Okeechobee, however, had high concentrations of readily available P (9.7 and 17.4% of TP respectively); hence, these sediments may play an important role in internal P cycling. The NaOH-P (Fe-Al-P) concentrations for Lake Okeechobee sediments were strongly correlated with amorphous and poorly-crystalline Fe (p< 0.01), suggesting that some P reactions in these sediments may be sensitive to changes in physico-chemical conditions such as redox potential and sediment resuspension.

Relationships between light availability, chlorophyll a, and tripton in a large, shallow subtropical lake

The relationships between planktonic chlorophyll a and mean light availability in the mixed layer were examined for Lake Okeechobee, a shallow eutrophic lake in south‐central Florida. There were significant spatial differences in the nature of this relationship. In the northern and central regions of the lake, concentrations of nonalgal suspended solids, tripton, were high due to muddy sediments and polymictic conditions. Light attenuation was predominantly correlated to the concentration of tripton and chlorophyll a concentrations were positively correlated to mean light availability in the mixed layer, Im. The western and southern regions of the lake had lower concentrations of tripton and light attenuation was correlated to chlorophyll a concentrations in summer and fall. Variables which estimate mean light availability in the mixed layer, such as Im, may provide insight into the role of light availability in the control of phytoplankton standing crop.

Seasonal and spatial variation in nutrient limitation in a shallow sub-tropical lake (Lake Okeechobee, Florida) as evidenced by trophic state index deviations

Seasonal and spatial variation in nutrient limitation in a shallow sub-tropical lake (Lake Okeechobee, Florida) as evidenced by trophic state index deviations

Seasonal changes in sediment and water chemistry of a subtropical shallow eutrophic lake

A field study was conducted (May 1981 to June 1982) to develop a data-base on seasonal changes of water and sediment chemistry of Lake Monroe (4 000 ha surface and ca. 2 m deep) located in central Florida, USA. This shallow eutrophic lake is a part of the St. Johns River. Quantitative samples of lake water and sediments were collected on a monthly basis from 16 stations and analyzed for various physico-chemical parameters. Relatively high levels of dissolved solids (mean electrical conductivity (EC) = 1832 µS cm1) prevailed in the lake water, and seasonal changes in EC were probably associated with hydrologic flushing from external sources, such as incoming water from upstream as well as precipitation. Average monthly levels of total N and P during the study period were 1.82 and 0.21 mg l−1, respectively. Nutrient concentrations in the water did not show any strong seasonal trends. Organic matter content of lake sediments ranged from 1 to 182 g C kg−1 of dry sediment, reflecting considerable spatial variability. All nutrient elements in the sediments showed highly significant (P < 0.01) correlations with sediment organic C, though little or no significant relationship appeared at any sampling period between water and sediment chemistry of the lake. Temporal trends in water and sediment chemical parameters may have been concealed by periodic hydrologic flushing of the St. Johns River into Lake Monroe.

Two new aphrotenian larval types from Chile and Queensland, including Anaphrotenia lacustris n.gen., n.sp (Diptera: Chironomidae)

AbstractTwo as yet unknown larvae of the circum-Antarctic subfamily Aphroteniinae, one belonging to Paraphrotenia cf. excellens Brundin, the other representing the new genus and species Anaphrotenia lacustis, are described. While the other members of the subfamily are confined to mountain streams, the larva of anaphrotenia has been found in the littoral zone of a shallow subtropical lake on Fraser Island off the coast of Queensland. Besides some peculiar specializations this larva attracts interest because of the primitive construction of the head capsule where the genae ventrally are widely separated and the wide medial interspace is occupied by a longitudinal postmental plate that is not fused with the genal margins. In these respects the Anaphrotenia larva stands out as the most plesiomorphic chironomid larva as yet known; and it comes probably rather close to the larva of the dipteran ancestor. With its closed head capsule and specialized mouth parts the predatory Paraphrotenia larva appears much more apomorphic. But it retains several comparatively plesiomorphous characters, and among the predatory species of the chironomid larvae it represents a very remarkable type. In both genera the crop is developed as a diverticulum from the oesophagus. The presence of a special, sac-like grinding mill at the caudal end of the crop in both genera seems to be unique. — The paper ends with a discussion on a comparative basis of some aphrotenian larval characters and their anagenetic status. Special attention is paid to the mentum and the development of ventromental and dorsomental teeth within Chironomidae. Also discussed is the independent development of predatory habits and their combination with special morphological traits within different monophyletic groups. Of special interest is the comparatively late occurrence of such habits and corresponding morphological traits high up in the chironomid hierarchy within the Harnischia-group, a phenomenon that is believed to be a case of evolutionary reversal.

Some studies on the ecology of limnetic crustacean zooplankton in Lake Begnas and Rupa, Pokhara Valley, Nepal

Monthly zooplankton samples taken during the period February, 1977 to February, 1978 in the deepest portion in two shallow sub-tropical Lakes, Begnas and Rupa in the Pokhara Valley, Nepal were studied. Four peaks of zooplankton abundance were noted. Adult and copepodid Copepoda were numerically dominant in both lakes with 56% Copepoda, 24% Cladocera and 20% nauplii in Lake Begnas and 48% Copepoda, 36% Cladocera and 16% nauplii in Lake Rupa. Other forms like Chaoborus larvae occurred sporadically in both lakes. An occurrence of the rare Limnocnida nepalensis (Coelenterata: Limnomedusae) in Lake Rupa was also noted during April and May, 1977. Although both of these lakes had already been ranked as eutrophic, the absence of calanoids, relative abundance of Bosmina longirostris and higher gross primary production in Lake Rupa is an indication of a higher trophic condition than that of Lake Begnas.