Ohlanga River's lagoon

The aim of this Earthcache is to give you a better understanding of Lagoons and the different types of lagoons that can be found around KZN (Please note we are referring to natural occurring lagoons and not man made lagoons for waste water management)

To start we need to know what a lagoon is so here is the definition taken from http://www.saltoflife.biodiversity.bg/ :” Lagoons are shallow coastal pools, which are fully or partially separated by the sea by a sand bar or by embankments along the coast. They may be linked to the sea by a narrow stream/opening.“

Interesting fact about lagoons is that their salinity or saltiness is different from that of the sea and may vary between slightly salty to super salty depending on precipitation (amount of rain witch bring fresh water down the river), evaporation and the amount of mixing with salt water during storms. This also explains the different types of organisms that inhabit them.

Coastal lagoons are more common than you might think, they make up approximately 13% of the global coastal areas. They are 1-3 m deep on average and almost never exceed 5 m deep. Lagoons always form around slightly sloping coasts which makes them highly dependent on the sea level, they are mostly located at water level height which makes lagoons highly vulnerable to even the slightest change in water level

1. Subsiding water may leave them completely dry

2. Raising water may destroy their separating barrier and flood them.

Geologically, coastal lagoons are young and ever changing systems. They have formed as a result of water levels raising mainly during the last 12000 years or so which is known as the Holocene period

Types of lagoons

Lagoons have a wide array of geographic and ecological variations. There are three main types, defined by the way they connect to the sea or ocean, they are:

1. These are connected to the ocean and a single, narrow opening. Usually these form along banks with high waves and substantial littoral drifts.
   
2. These are larger and usually run parallel to the coast. They connect to the ocean via one or more openings. The water circulation in this lagoon type is dominated by the tides and wind.
   
3. These also run parallel to the coast, with multiple openings. These form around coasts where tidal flows are strong enough to prevent silting caused by waves and by littoral drifts. The water in these lagoons tends to move toward the sea.
   

Questions

1. After reading the cache description What type of lagoon would you say this lagoon is, give reasons for your answer

2. If you had to guess (don’t advise tasting as I do not know the contaminant levels in the water) which would you say is more salty at this location – the sea or the lagoon – give reasons for your answer
3. In your opinion do you think that the lagoon life near GZ is in danger due to human interference? Why do you say so?
4. When you walk from the Parking towards GZ you walk along a sandspit. Is this sandspit getting bigger due to deposition or smaller due to erosion? Give a reason for your answer and also state what the long term implication is to this area?
5. (Optional) take a photo of something that you found interesting around the Lagoon and include it in your online log

Please send your answers via the geocaching messaging system or via email from our profile

Hope you enjoyed the walk and the Earthcache