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Deal, Robert

Kantz, John A.

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Algal and Lemna populations♦  61Algal and Lemna populations continue to fluctuate seasonallyand basin-to-basin in the Olentangy River wetlandsRobert Deal and John A. KantzDepartment of Natural SciencesShawnee State University, Portsmouth, OhioIntroductionPopulation densities and species composition of thephotosynthesizing components of the two research Wetlandscontinued to be in a state of seasonally dynamic changeduring 2000 — just as has been the case each year since theOlentangy River Wetland Research Park began operation in1994.  As noted in the two most recent of our annual reports,Lemna minor, ‘duckweed’, appears to have become animportant determinant in how much filamentous algae(herein referred to as ‘macroalgae’ and ‘mat algae’) ispresent in the summer and early fall in the surface water ofthe basins and shallows of both Wetlands. However, thisinfluence does not appear to always be the same whencomparing Wetland 1 (originally planted with vascularplants) and Wetland 2 (originally unplanted). In otherwords, environmental factors, some apparent, some not,influence populations of both the macroalgae and duckweed,but not necessarily in the same way for each.Interaction between duckweed and mat-forming algaecan be much better documented by visual observation ofeach of the three basins in each of the two experimentalWetlands than by microscopic analysis of small samplesfrom each basin. Consequently this approach to the algalsurvey was given added emphasis in 2000.  Detailed visualobservations were made on the extent of algal mat andduckweed coverage on seven dates (Apr. 1, May 13, July16, Aug. 25, Sept. 19, Oct. 13 and Oct. 20) during thegrowing season. Samples for microscopic determination ofgeneric composition and analysis of microalgal diversityand abundance were collected on four of those dates (Apr.1, May 13, July 16 and, Oct. 20). Naturally, moreobservational and sample collection events would havebeen better, but this was not possible because of our distancefrom the site and the increasing primary workload.MethodsObservational data was obtained by carefully lookingover the surface of each of the three basins and the twoshallow areas separating those deeper basins in each ofWetland 1 (W1) and Wetland 2 (W2). The density andextent of coverage of each component – Lemna, Potamegeton(pondweed), and the genera of macroalgae that can bedetermined by appearance, texture and feel,  (Cladophora,Hydrodictyon and Spirogyra, in particular) – were estimated.These observations are condensed below under the heading‘Visual Observations’.The methods of sampling, microscopic analysis andrating for abundance on the survey microscope slides ofalgal populations in the Wetlands have been outlined severaltimes in previous annual reports (see ‘Summer matmacroalgae largely replaced by duckweed, Lemna minor, in1999 in two Olentangy River experimental wetlands’ in the1999 edition of this publication) so will not be repeated here.Statistical analyses (t-test) of the seasonal meanabundance in W1 vs. W2 in 2000 of four common genera,Chlamydomonas, Cladophora, Spirogyra, (Chlorophyta)and Oscillatoria (Cyanobacteria) were made on each of theabundance ratings (scale) determined from the four sets ofsamples analyzed microscopically. Also, the abundanceratings for all of the genera of each of the algal DivisionsChlorophyta, Chrysophyta, Euglenophyta, and Cryptophyta,and the Cyanobacteria that were identified and rated forabundance in W1 and W2 were compared for each of theyears 1995 – 2000.  Additionally, the abundance ratings ofall algal and Cyanobacterial genera were combined andcompared en-mass, W1 vs. W2 for each of the same years.Results and DiscussionVisual Observations Supplemented withMicroscopic DetailsApr. 1, 2000:  On this date there was no floating algal matin any of the Wetland basins.  Because of the high, muddywater in the Wetlands it was not possible to locate andcollect any of the small, floating clumps of filamentousalgae such as had been seen in early spring in most previousyears. For the same reason surveying for any bottom algaewas impossible.  As a consequence of these conditions onlyplankton net samples were collected. The colonial algaTetraspora, which in 1999 was found in samples for the firsttime since the study began in 1994 (in both Wetlands 1 and2) was present in the samples from inlet, mid and outletbasins of W1 but was not found in any of the samples fromW2.May 13, 2000:  By this date algal mat coverage in bothWetlands was visible, but in distinctly differing amounts.Both Wetlands had limited amounts of floating, filamentousalgae in their inlet basins (estimated at less than 10%coverage in each), but the mid basin of W1 was about 65%62  ♦  The Olentangy River Wetland Research Parkcovered with a mat composed primarily of Cladophora andRhizoclonium whereas the same portion of W2 had onlysmall floating clumps of the same genera; these clumps onlycovered an estimated three percent of the basin.  There wasa small amount of Hydrodictyon visible in the outlet basinsof both Wetlands and a small amount of Tetraspora was stillpresent in the outlet area of Wetland 1.  Duckweed wasevident in light to moderate densities, especially in the areasclose to the shores of the basins and in and adjacent to theshallow areas lying between the basins of both Wetlands.July 16, 2000:  Prior to this collecting date there had beena high-water event that left dried algae hanging from thesupport posts of the boardwalks and cattails of the shallows.Surface coverage of all basins was heavy and consisted of amélange of mat algae (mostly Cladophora), growingintermingled in portions of inlet and outlet basins with thetops of Potamegeton and overlain by a top layer of Lemna.Small patches of other vascular plants were present here andthere. In both mid and outlet basins there were scatteredareas of a thin, green surface film; later microscopicexamination revealed that this was composed entirely ofEuglena. Microscopic examination of the mat samplesrevealed typically high summer-time diversity of algalgenera, this was especially true of those samples from theoutlet basins where as many as 18 genera of the Chlorophytawere found under a single 22mm2 coverslip.  Strong outflowfrom the flooding apparently flushed most of the filamentousalgae out of the upper portion of the drainage swale; collectionfrom the spillway wall was all that was possible.  Microscopicexamination later identified Cladophora, Rhizoctonia andOedogonium as the filamentous components.Aug. 25, 2000:  Only visual observations were made onthis date (no algal collections).  Both inlet basins werealmost completely covered with a thick layer of Lemna; nofilamentous algae could be found except for that attached tothe boardwalk support posts (previous microscopicexaminations have shown that Oedogonium is the typicaldominant in this microhabitat).  There was a noticeabledifference in the coverage of the mid basins.  W1 had about25% coverage by Lemna whereas W2 had about 70% suchcoverage.  Cladophora-dominated mat covered about 60%of mid W1, but only about 20% of mid W2.  In both of thesebasins the algae was overlain by a light to moderate densityof Lemna.  In the limited surface area (W1 ca 15%, W2 ca10%) of more or less open water there were small clumps offloating Cyanobacteria intermingled with scattered Lemnaplants.  There was also a noticeable difference in the surfacecoverage of the outlet basins.  W1 had about 50% essentiallyopen water with small, scattered clumps of Cyanobacteriaand thinly scattered Lemna.  Also visible here were somebottom clumps of Spirogyra.  The balance of this basin wasdominated by intermingled Potamegeton and filamentousalgae; this was estimated to consist of about 80% Cladophora/20% Spirogyra. In contrast, outlet W2 had only about 5%open water, 75% coverage by a Cladophora-dominated matoverlain by moderately dense stand of Lemna, and about20% of its area occupied by small-medium (2-10 cm)clumps of Cyanobacteria.  None of the film of Euglenaobserved on 7/16 was observed.Sept. 19, 2000:  The amount of Lemna was less in bothinlet basins than was observed on July 25 and it waspossible to again locate filamentous algae.  Both mid basinswere observed to still have considerable duckweed coverage.The difference in abundance of mat algae and other surfacebiota seen in August between mid and outlet basins, W1 ascompared to W2, had persisted (see above) with the mostnoticeable difference being a significant increase in thedensity of duckweed in the outlet area of W2.  The swalestream had an abundance of Lemna along its edges and verylimited amounts of filamentous algae.  As in August visualobservations were made with no samples for microscopicobservation being taken.Oct. 13, 2000: Inlet W1 still had a heavy covering ofduckweed over a portion of the basin whereas the inlet ofW2 had only a generally light covering; some of thisdifference was due to the obvious difference in surfacewinds over the two basins as these were influenced bydifferences in the stands of vascular plants around theperimeter of the two basins.  In the mid basin of W2 theduckweed was so heavy that no filamentous algae could beseen; the algal mat that had been prominent in mid W1 in theprevious three months appeared to be disintegrating asmost of the filaments of Cladophora appeared to be senescentor dead. The Cladophora that was observed in the outletbasins was also in a deteriorated state.  The density ofduckweed in these basins was noticeably lower than in theprevious month. The swale channel was essentially openwith minimal amounts of filamentous algae and duckweedalong its edges.  As for the previous three dates (above) nosamples were collected.Oct. 20, 2000:  Observations were made and samplestaken this date.Duckweed, though still abundant in places, appeared tobe deteriorating and there were many bleached plants in anycollection of this vascular plant.  In the areas of open waterit was possible to see patches of the former algal mat restingon the bottom; in other places Spirogyra appeared to beincreasing, as compared to the week before, in numbers of‘clumps’ on the bottom of open water areas, this replicatedan aspect of algal life seen in previous years.2000 Microscopic SurveySixty-nine genera of algae and Cyanobacteria wereidentified microscopically from the four sets of samples; 59were found in W1, 60 in W2 and 31 in the swale (Table 1).The total of 69 genera derived from four sampling dates in2000 compares with the 76 genera identified in seven setsof samples taken in 2001. Three genera, Crucigenia andChaetosphaeridium (Chlorophyta) and Synechocystis(Cyanobacteria), were identified for the first time in theWetlands; this brings to 143 the total number of genera ofalgae and Cyanobacteria that have been identified in theAlgal and Lemna populations♦  63two Wetlands and drainage swale since the survey began in1994.The statistical analyses demonstrate that on a seasonalbasis there were no significant differences in the abundanceof the common genera Chlamydomonas, Cladophora,Spirogyra and Oscillatoria. Such ‘pooling’ of the abundanceratings derived from microscopic survey based upon smallsamples all taken from the wetland board walks ignores thelarger picture that specimens of a macroalgal genus can beseen at a location in a wetland basin but not be reachable forsampling or that the random (scattered) small samples thatare taken may simply miss an alga that is present.The comparison of the seasonal abundance of the generaof each of the four Divisions of algae and the Cyanobacteriaindicated that on a Division–by-Division basis there areonly small differences, none significant, in the overallabundance of algae surveyed season-to-season in W1 ascompared to W2, 1995-2000.  This information does moreto indicate that there is internal consistency in the samplingand microscopic survey procedure than it says anythingabout the noticeable differences that can be seen visuallyand microscopically when comparing one basin with another,both intra- and inter-wetland. With our increasing experiencein surveying the Wetlands it appears, as said above, that thebig differences are better documented by careful visualsurvey of each basin of each wetland.  The microscopicsurvey provides the information on the presence/absenceand abundance of the many genera of microalgae thatappear (and disappear) in the wetlands.

Algal and Lemna populations continue to fluctuate seasonally and basin-to-basin in the Olentangy River wetlands

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Algal and Lemna populations continue to fluctuate seasonally and basin-to-basin in the Olentangy River wetlands

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