Long Term Time-Series Data on Aquatic Macro-invertebrates Monitoring by Okavango Research Institute, Botswana

Study Extent

The monitoring sites (Lake Ngami, Chanoga-Boteti, Thamalakane-Maun and Nxaraga – ORI Camp) are georeferenced locations in the south eastern part of the Okavango Delta, Botswana. They were systematically selected to form part of an ongoing monitoring exercise conducted by the Okavango Research Institute (ORI). The sites albeit limited in their nature to represent the whole of the Okavango Delta ecosystem, in terms of MI distribution, they are representative of areas such as seasonal swamp (Nxaraga) occasional pools (Lake Ngami) and drainage rivers (Chanoga and Maun).and. The monitoring surveys provide baseline information on macroinvertebrate assemblages and environmental conditions at these sites. Lake Ngami is an occasional endoreic shallow reservoir at the southernmost part of the delta. It is usually regarded as highly productive zone when inundated. The lake started filling up in 2004 after a 30 year dry spell. When the MI surveys started in 2017, the lake was drying up, and virtually inaccessible. Therefore there is no data in this resource, but in future, lake samples will be included. Thamalakane-Maun (later referred to as Thamalakane) is one of the draining channels of the Delta-located downstream of the confluence of Boro and Gomoti distributaries. It flows through Maun which is moderately populated (pop. 50,000+). Maun presents likely conditions for pollution , human activities such as, fishing, washing , abstraction and other disturbances thereby potentially introducing (a) change(s) in environmental requirements for MI assemblages in the Thamalakane River. The site therefore, offers representation for likely polluted systems in the Delta, and provides comparative study/site to other sites -such as Nxaraga- which is somewhat untransformed. Chanoga-Boteti (later Chanoga) is a lotic habitat located approximately 30km east of Maun, on the eastbound drainage of the Thamalakane River-the Boteti. The lagoon is flood pulse fed with varying flows , volume and extent consistent with the seasonally flooded lower Okavango. The monitoring surveys are conducted on monthly basis and the data a intended for abundances and species diversity. However, it is not possible to conduct the surveys due to a number of reasons. Key among these is the fact that the lower southeast delta is mostly seasonal swamp and occasional pools. Meanwhile, the flows in these areas are highly variable in volume, extent and duration of inundation-meaning that some months and some sites will be dry and therefore no samples will be unavailable. For example, there are no samples for Lake Ngami at the publication of this resource, while other areas will have some gaps.

Sampling

As recommended by Mosepele and Dallas (2007), the primary motivation for sampling is to ensure that a variety of available aquatic habitats within each of the three focal sites (Nxaraga, Chanoga and Maun ) were sampled. Nine micro-habitats were identified; marginal vegetation in channels; marginal vegetational in lagoon; marginal vegetation in backwater areas joined main channel; inundated floodplain areas; floating vegetation either in channels or lagoon; floating vegetation. Sampling of macroinvertebrate assemblages from each habitat is undertaken using a one net, a D-net (1mm mesh) 30cm x 30cm square frame. One person sampled each habitat intensively for 2minutes by sweeping net through the vegetation, grass or in water. Given the variation in habitat type and accessibility to different habitats, sampling is standardized as sampling effort (per time). Two minutes is considered sufficient to collect the variety of aquatic taxa associated with particular habitat. All material collected in a net was sorted on site, using large sorting trays, taxa in each tray were identified for 30minutes per biotope, or after 5 minutes have elapsed since a new taxon was last identified. Abundance of all taxa is then estimated using the following scale: 1 = 1 individual, A = 2 to 10 individuals, B = 10 to 100 individuals, c = 100 to 1000 individuals, D = over 1000 individuals. Taxa were identified in the field to the family level.

Quality Control

The sites are georeferenced. All taxa were identified in the field mostly to family level and some other specimens were collected and preserved in 70% ethanol. The taxa were further separated and identified to morphospecies which were verified in the laboratory and identified to genus where possible. However, certain groups were not identified beyond class. “Aquatic Invertebrates of South African Rivers” Illustrated by A Gerber and MJM Gabriel was used as a guide to identify taxa in the field.

Method steps

1. Materials: Boat D-Net Stopwatch Notebook Pen, pencil Magnifying lens Droppers Tweezers Identification manuals Vials Sample trays Sorting trays
2. MI Sampling • One person intensively samples the habitat for 2 minutes by sweeping the net through the vegetation. Four separate areas are sampled for 30 seconds each (total time sampled = 2 minutes) to ensure that the full spectrum of areas (and both sides of the channel) and vegetation are sampled. If the vegetation is in flowing water then the net should face into the current so that dislodged organisms are captured in the net • The vegetation is rinsed in the net to remove fine particulate matter, and then tipped into the sample tray. The net is checked for any organisms attached to it, which are removed and added to the sample tray. If there is a large amount if vegetation in the sample, it is rinsed in the net before sorting. • Representative organisms from all macroinvertebrate taxa observed in the sample tray are removed from the sample tray and place in the sorting tray. • Each sample is searched for approximately 30 minutes or until 5 minutes has passed since a new taxon is found. For samples that have a large amount of vegetation present, it may be necessary to do the searching in stages. • At each sampling point, in situ measurements should be taken of pH, conductivity, dissolved oxygen and water temperature.
3. MI Identification • Macroinvertebrates are identified to family level in the field, with the exception of Turbellaria (Flatworms), Annelids: Oligochaeta (Earthworms) and Hirudinea (Leeches), which are identified to a higher taxonomic level, and Coleoptera: Mixed beetles, which are the combination of several beetle families including e.g. Dytiscidae, Noteridae, Sperchidae. • Any taxon for which the identification is uncertain is collected and identified in the laboratory under the supervision of ORI. • One or two individuals of each taxon recorded on the field datasheet are collected and placed in a sample vial. This is preserved with 70% alcohol, labeled with the Site Code, Date, Aquatic Vegetation Code and Assessor Name. The sample and datasheet are sent to ORI for quality control and curation. • Once all taxa have been recorded and representative organisms collected, the tray is checked before discarding the sample by slowly and repeatedly emptying the tray and checking for any organisms that are stuck to the bottom of the tray.
4. Data Production • The field datasheet is completed with the following information recorded: Site Code, Site Description, Date, Time, Assessor and Water Chemistry. The aquatic habitat sampled is ticked The georeference (GPS co-ordinate) is recorded if sampling is being undertaken at a new site. • All taxa present are recorded on field datasheet. Each taxon is given an abundance value based on the rating scale: 1 = 1 individual, A = 2 to 9 individuals, B = 11 to 100 individuals, C =101 to 1000 individuals, D = > 1000 individuals. The sample and datasheet are sent to ORI for quality control and curation. • Later the datasheets are transcribed and stored as soft copies (in Microsoft Excel). The files are later formatted to create event files and occurrence files according to DarwinCore standards, which are kept as flat files (.csv, .rtf formats) before sharing.

Most aquatic macro_invertebrates were identified up to family level

1. Atyidae
   common name: Fresh water shrimp rank: family
2. Belostomatiidae
   common name: Giant water bugs rank: family
3. Naucoridae
   common name: Creeping water bugs rank: family
4. Notonectidae
   common name: backswimmers rank: family
5. Gerridae
   common name: pond skaters rank: family
6. Veliidae
   common name: ripple bugs rank: family
7. Pleidae
   common name: pygmy backswimmers rank: family
8. Nepidae
   common name: Water scorpions rank: family
9. Libellulidae
   common name: dragonflies rank: family
10. Aeshnidae
    common name: dragonflies rank: family
11. Zygoptera
    common name: Damselflies rank: order
12. Diptera
    common name: Flies rank: order
13. Mollusca
    common name: Snails, limpets rank: order
14. Ephemeroptera
    common name: Mayflies rank: order
15. Trichoptera
    common name: Caddisflies rank: order
16. Odonata
    common name: Dragon flies rank: order
17. Hemiptera
    common name: Bugs rank: order
18. Coleoptera
    common name: Beetles rank: order

Monitoring sites along the lower panhandle, south eastern distributories of the Okavango Delta.